Try to use setblock in the RTX beta and the game will crash after you begin type the Z coordinate. You don't even have the chance to specify the block, the second you type a digit for the Z coordinate, it crashes. Is tab completion segfaulting on setblock? tp has similar syntax for coordinates and does not crash. It happens in The Observer and Aquatic Adventure RTX as well as non-RTX marketplace worlds such as Catastrophic Pandamonium, but not a regular world.

Edit: Fill crashes too on the 2nd Z coordinate. Probably the blocklist being broken in marketplace worlds. Give does not crash.

Edit 2: Pure speculation but is this because of the unimplemented fungus blocks or is that pure coincidence?

Edit 3: This happens in the regular beta for 1.16.200 too.