I installed MC26 on a new Mac with Big Sur 11.0.1. I get a tagging error when I attempt to Rename, Move and Copy Files.
Media Center encountered errors while tagging or moving files. Check that the files exist, are not read-only, and are not in use by other programs.
Tagging error: /Users/eds/Downloads/01. Prologue - Loreena McKennitt.flac
Edit:
Not an OS permissions problem. I am able to convert to the same directory that I was trying use for Rename and Move. Conversions are even able to create subdirectories.
This is a Mac with a new M1 chip if that has any bearing.