it was custom (which is why you need to unlock the bootloader) as 4.2.2 or something was the last official release. i got it working in the end. i did notice some suggested android 6 was less laggy, but went with the most recent version. the guides were a few years old. the tablet is about 12 years old and only has 1gb ram. i just did it because i could. they had £60 refurb 10" fire tablets recently, so it would make more sense to use one of those unless you are really financially strapped. it was for an older person who wasn't using it as it was too heavy and i set up a 7" fire tablet for them, but they found it a bit small by comparison so i was going to get them to see if they prefer the 8" or 10" fire instead as i can give them those to pick from and they will be more up to date and usable, and a bit lighter than the samsung. i just rest my tablet on my knee so dunno why they don't