Extremely poor performance with m4b audiobooks

When trying to retag some audiobooks in my collection, I noticed the poor performance with m4b audiobooks. Tagging works fine, but saving takes a lot of time.
A folder of about 100 audiobooks took several hours just to save.
The bigger the file is, the longer the save time.
Is there anything that can be done about this?

Many thanks, keep up the great work :slight_smile:

Been a while - in the meantime I got a new MacBookPro and am running Monterey instead of Big Sur now.

Still the problem persists.

Am I the only one affected? :face_with_raised_eyebrow:

Can you share one of the files with such bad performance privately via iCloud?