DO NOT USE 1.19!
1.21.1, 1.20.4 and 1.20.1 are perfectly fine i guess.
Check out the gamerules
All blocks are decorative, the dimension needs a key tat can be picked only in creative but some of the blocks is avaible in snowy & icey zones..
To get to the rotten dimension you have to find a cold biome, then search a flesh village or just some flesh block, and make a portal with the blocks you got. (only flesh blocks works)
Or you can just start already infected and spread the flesh by yourself.
