Testing in 5.1.4-beta1 on 1.21.0 and 1.21.2-rc1

1.21.0 is affected, 1.21.2-rc1 is not.

I thought this might be what d2a2ebf fixed but that was from before beta1 was released, so perhaps not?

The commit you mentioned was indeed fixing this issue, but I didn't check the earlier versions.

It looks like the item_model component does only exist since 1.21.2, which I didn't expect (and the wiki doesn't list it properly which I'm fixing now :D). Looks like I have to go back to custom model override which is unfortunate.