Maps that are placed in a item frame that has pinned locations show the text through walls. This behavior is new to the latest pre-releases, and does not affect 1.21.1.
Steps to reproduce:
Place down a renamed banner
Use a map item on it
Place the map in an item frame
Place blocks in front of the item frame
1.21.2 Pre-Release 3:
[media]1.21.1:
[media]