Left/Right and Up/Down arrows jump to wrong thumbnail.
(beta 188.8.131.521 on M1 silicon Mac)
In a multi-level folder hierachy with 20+ thumbnail images/folders at each level, use the arrows and command (Apple) key to navigate. CMD-Down to get into a folder, and CMD-Up to come back up a level. Go down, and use the Left and Right arrows to move through images, then pop back up a level.
Now use the Up/Down keys by themselves (no CMD) and they don't work at all.
Go down a level and back up again. This time, use Left or Right and your selection will pop to an unexpected place in the thumbnail gallery.
Hello, Bridge 13.0.1 has native M1 suppport, and many issues have been fixed. You should upgrade to that version, but be informed that while it supports a modern UI with multiple content tabs, it has for the moment lost the multiple windows feature. It might be wise to keep a copy of V12 if you need that feature.