current version is 1.20, but recent record use ver 1.11.11, even NMG speedrun also use 1.11.11.

What are the advantages of this version? Why is no one using the current version?

this is just an issue of updating the list of available version (by any mod). in the video you may be able to spot the version actually used.

Also 1.2 has only been out for a short while and does not have any advantages or disadvantages over 1.11.11 so a lot of runners just haven't gotten new pbs on the new version

maybe 1.11.11 is nothing, but Pincer Glaive is more powerful in 1.11.4 because is can stack 2 poison not 1 in this version. So 1.11.4 is the best all boss speedrun version?