Please let me know the following: Your OS whether just IMAP, POP, or both whether you has thunderbird set to clear trash on exit

We have an active bug on this and that info will help. Thank you.

Are you sure you are running 115.10.1? 115.10.0 is known to have that problem (won't restart because it never shutdown all processes cleanly).

To be more exact, TB 115.10.0 has a bug where restart may not occur due to leaving those processes you see still running after shutdown. However, this is thought to only happen if the server setting "Empty Trash on Exit" is configured for IMAP servers. TB 115.10.1 is supposed to fix the problem. Re: https://bugzilla.mozilla.org/show_bug.cgi?id=1891889

For me, 115.10.1 did fix the problem. I use the Empty Trash on Exit option for an IMAP server.

Yesterday (and before) I was seeing the problem of the processes not shutting down and preventing Thunderbird from restarting. My systems updated Thunderbird this morning to 115.10.1 and the problem has been resolved on both systems here.

On startup 115.10.1 is asking me to set up your existing email address, even though it worked fine yesterday. No matter what credentials I give for 3 different accounts it fails.

FS, Can you be more specific on the error you are seeing and what you are doing when you see the error?