If a friend joins your world (or you his) there is a bug with right clicking. Depending on the block, right clicking changes the materials (grass turns to torch, grass to terracotta etc). Only the extra player can do that (you can play normally) and it is only visual (lava on the nether turns into kelp but still you get burn if you walk on it) and visible to your friend. Also as seen in my screenshot, different types of axis start to appear under certain conditions. The bug also affects commands like open/close doors etc. It seems that some new materials from the 1.17 update appear also as well as a material saying Update on it (on haystacks)