I have noticed that, in the current beta 1.17.30.24 axolotls do not spawn.  I have explored a lot of the world and seen no axolotls. I have also set up a spawning box per the requirements for axolotls to spawn: 1) Below X 63; 2) Water sources only, no flowing water; 3) Solid blocks above and below water; 4) Complete darkness; 5) Tinted blocks on all side so that I could see spawning. I afk'd 30 blocks away (sim distance of 4) for an hour. NO axolotls spawned.