According to an internet platform (blueray-disc.de) the original BDs are all MPEG-4/AVC
I thought earlier discs were MPEG2.
Wikipedia agrees with you, @sam_nazarko:
MPEG-2 was used by many studios (including Paramount Pictures, which initially used the VC-1 format for HD DVD releases) for the first series of Blu-ray Discs, which were launched throughout 2006.
There seems to be a misunderstanding here:
I was trying bluray disc isos of three different blueray discs with osmc. All these three discs were encoded with MPEG-4/AVC, according to the internet platform that I mentioned.
I didn’t want to state that all blueray discs are encoded with this codec.