Blocks/items cannot be normally used while targeting a fully charged respawn anchor

Shift-click to use items/blocks on the respawn anchor.

I would like to request a reopening of this ticket, because of MC-133691, in which full cauldrons had the same issue, which was considered a bug and fixed.

Cauldrons are only interactable with certain items though. It's similar to the composter.
You can always interact with a fully charged anchor, so I don't see why this wouldn't be intentional. The same thing applies to beds, for example.