Re: "Mail takes a LONG time to quit
I've used Apple Mail for years, but over the last year it has started taking a very long time to quit. I thought the problem might go away with the new Tahoe app, but it didn't. Any idea what could be causing this?"
Activity Monitor may show what's happening ...
See how to: View information about Mac processes in Activity Monitor - Apple Support
You may have years of messages and lots of Mailboxes. Mail may be busily updating Mailboxes.before quitting.
or
Sometimes there can be interference from un-necessary third-party-apps, like virus-checkers, ad-blockers, cleaners, and the like ... even VPN. Try turning them off, or use uninstallers from their developers.
Any third-party apps or browsrs etc. you find necessary need to be kept up-to-date to remain compatible.
Now that we can have multiple desktops ("spaces") open, and swipe easily between them, some of us rarely quit frequently used apps. No waiting to close one app, and then waiting for another app to open, is necessary.
If interested: See how to: Work in multiple spaces on Mac - Apple Support