Ok Enmanuel, agree) So, if you are interested I'll join there, my fav race.
So 24 hours Le Mans is not the category or champ, it is the race that is organized historically by ACO and, in different years the part of sportscar championship under the FIA (but there were also the periods when it was the separate race and wasn't included in any champ).
The idea of 24 hours of Le Mans initially was to race the cars, expensive ones, but those the buyer is able to buy. So it was like the marketing tool for manufacturers to show the quality and reliability of the cars they produce. Race on Sunday, sell on Monday. So, historically, sportscars bear (or beared for a long time) some key requirements. The cars must have the lights, have 2 seats and, till mid 70's - have a capacity for a spare wheel (it was formal approach, in reality there were fake wheels to save the weight). So, in 20,30,40 and early 50's there were the grand prix cars for sprint races - monoposto with open wheel (except W196R for Monza and Dijon and pre war formula libre rekordwagens), which later became F1 and 2 seat closed wheel sportcars.
Later on, from mid 50's sportscars, of course with the help of giant budgets from Jaguar and Mercedes, started to transform into prototypes - sportscars formally, but in reality pure race cars that had no omologation (production based sibling). Mercedes 300 SLR and Jag type C can be called as first Le Mans pure prototypes. Later on Ferrari has joined in building prototypes, the cars mostly had nothing in common with the production cars. Usually used modified F1 engines with higher capacity and lower revs (so nothing close to production). To fight with the growing speeds, the FIA has separated the leading class of sportscars (we dont talk about the pure production cars which were always the part of sportscar racing, we talk about win pretenders, top tier). There were the 3 liter prototypes and sportscars which had to pass the omologation (but no engine capacity limit). So, the best example of this case Ford GT40 which had 7 and 4,9 liter V8 and 3 liter Ferraris 312P, 330P and so on. Ford GT40, being formally the production car, was in fact the pure race car as a 3 liter prototype. It was always the question in Le Mans which car can be considered pure race car and which is production based)) - all depends how you read the rules and are you ready to invest heavily to build 50 or 25 pure race cars (for omologation reasons). In late 60's Ford could spend. Simply imagine building 50 race cars that are 2-3 times more expensive than comtemporary F1 machinery :-)
Later on FIA has introduced new regs. These were group 1,2,3,4,5,6,7 cars and F1. Group 1-4 production based cars, Gr 5 omologated race cars with 5 liter engines, group 6 3 liter protos (no omologation required), Group 7 - Formula libre - the only requirement - 2 seats and 4 wheels))
The top category of Le Mans and sportscar champ consisted of the cars like Porsche 917 and Ferrari 512 (both group 5 - formally production cars, because of omologation, but in reality pure race machinery) and cars like Ferrari 312P and Alfa 33 (gr6 protos with basically 3 liter F1 engines and porsche 908/03 fr6 cars that was used by factory to fight for win on twisty tracks - very successful). Group 5 proved to be much faster (also faster than F1 despite higher weight) and was eliminated by 1972, gr 6 continued its way up to 1974. Group 7 never raced Le Mans, these were the hill climbers from late 60's weighting 380-450 kilo and Can Am monsters - like 917/30, or mclaren M20. However, in 1970 Porsche and Ferrari raced in can am with gr5 cars. Porsche - sometimes successfully
In 1975-1976 group 5 has changed, it became the silouette class (aka porsche 935 - racecar but with serial car elements - f.e. production central body section). gr 6 remained as prototype (see porsche 936). Speeds between them were close, but the difference was distinct. If previously you could build more powerful car, but you had to omologate it, now you had to have production based parts for the formally lower class.
After all this mess with groups, FIA has introduced by 1981 3 sportscar groups (not 7 like previously). Group A - production based cars, Group B - you know, i am sure)) and group C - sportprototypes without omologation, the only production based part - engine block (not head, only crankcase). The only performance limitation - certain amount of fuel that can be used during the race distance. Like late 60-early 70's -the golden age of sportscar racing. Great variety of engines, from porsche 2,6-3,2 liter high boost turbocharged B6 up to 7 liter atmo Jags. There were also C2 class for small protos - cosworth or small production based engined cars.
Starting to compete with the F1 in terms of popularity, by 1991 under the pressure from Bernie, the high class was separated once again. Group C was separated to C1 - 750 kg 3,5 F1 engined protos and highly ballasted, previously 850 and now 950-1000 kg old school C2 protos with free engine capacity (but as previously mentioned production based crankcase). you see historical spiral with Gr5 and Gr6 from 70's, yes?:-) Old C2 philosophy cars prooved to be faster and more reliable, so they were totally eliminated by 1992. In 1993 because almost all competitors went to F1 (that was Bernie plan) Group C died. In parallel IMSA (american sibling of FIA sportscar champ also raced group C cars, but the were a bit different). No fuel restrictions and higher downforce cars (up to 4,5 tons of DF in early 90s at the speed of 200 mph)
Later on there were some private protos (not very tech advanced and based on old constructions) and GT1 cars that started to fight for win - real production cars, like Porsche 911GT1, Mclaren F1, Ferrari F40 GT. By 1998 GT1 cars stopped to require omologation so they became the prototypes, but formally GT1 cars. By 1999 it became LMGTP - Le Mans GT Prototypes (example Mercedes CLR and previously GT1, now LMGTP Toyota TS020). Closed cockpit cars, look like serial, but pure prototypes and open cockpit cars - LMP - BMW v12 LMR. In 2000 once again - new regs. LMP900 - high tier protos wighting 900 kg (AUDI R8, private BMW V12 LMR, Front ford engined Panoz LMP1), small LMP675 (675 kg LMP2 cars - like Lola GM), GT1 - now purely production supercars like ferrari 550 and GT2 - Ferrari 360 and 911
In 2006 it became LMP1, LMP2, GT1 and GT2. LMP1 - Audi R10, Peugeot 908. LMP2 - Porsche RS Spyder (now 750 kg). In Imsa due to balance LMP2 was even faster in twisty tracks.
Later on, you possibly know - LMP1 H, LMP1 (non hybrid), LMP2 (now cost capped gibson engined cars), GT Pro and Gt Am. Those LMP1 were tech avant garde cars, potentially faster than F1, higher technology cars (once again history spiral with Gr5-Gr7 cars). Due to inability of ACO to provide the ROI required for such high tech the new Hypercar class was introduced (much cheaper version of LMP1H with production based e-machines and closer to production engines)
So we are now here. Hypercar class is separated into LMH (FIA cars) and LMDH (IMSA cars). Both are limited to 500 kw (670HP) and lift drag coeff -4 to1. Power is constant, with or without e machine. When e machine works the ICE decreases the fuel consumption and loses the power. What is the difference?
LMH e machine is located at front. LMDH e machine is located on the rear. LMH can activate it only after 120 kph, LMDH any time. LMH chassis is own built, LMDH chassis must be built by 1 of 4 omologated manufacturers that built cost capped LMP2 cars (Oreca, multimatic, dallara or Ligier). Both versions of Hypercar will race against each other in FIA champ , In america only LMDH.
So, sorry for grammar, but I tried, very briefly, to put you through the sportscar history to the point where we are now. Sportscar history is much more difficult than F1 and very non linear, thats why additional reading will help you.