Lightroom Classic: Unable to Simultaneously Read and Write

I believe this is a limitation of the LR catalog database structure.

What you can do is to add your metadata updates to ALL of the files first including adding a unique identifier keyword, such as 20200202_save_metadata_to_file. Then select 'All Photographs' in the Catalog panel and then use the Filter Bar Text Keyword filter with the above unique keyword. Select ALL files (CTRL+A) and Save Metadata to File (CTRL+S). You can then remove the unique keyword from all of the currently selected files.

After thinking about this I suggest not removing the unique keyword with DATE. That will cause a metadata conflict. The keyword is also helpful to identify files that have already been updated as you search for other files that remain need to be updated.

Another workaround idea is this.  Turn off "automatically write changes to XMP" in Catalog Settings.   Then do your copyright and other metadata changes along with your imports or whatever else you want to do.  Then just before you go to dinner or go to bed flip the preference back on to automatically write changes to XMP and it will then catch up on all the pending metadata changes.