By popular demand, the Wheelchairs mod is now in the process of updating its content for 1.21.4!
Only the wheelchairs, wheeled stool, and speech tablet are currently available. The chairs are missing a couple of upgrades and the tablet its GUI background texture, but this otherwise represents the most stable content currently up-to-date.
Most of the disabled content can still be accessed with commands or item mods but is either missing functionality or can cause crashes, potentially even bricking your save entirely if misused.
For obvious reasons, I don't recommend fiddling with most of it, and it's only still present at all because it'd be even harder to actually remove it from the codebase entirely.
More content to be re-enabled as development continues.