Hi all,
since this is the first Google-Search result i found and it did not help, I write a solution that helped with my problem since there is no other real solution listed here. This is on Desktop-Client 3.14.1 on Win11. After I put on some foulders to sync with the server, my client started crashing after win11 Boot. Just found out today that it crashes when it starts sync. My Global Network Settings on Nextcloud were on Auto-Limit. This seems to have trouble with my Windows Internet drivers. While crashing on sync, this was the first i changed. After setting manual limits for Up and Download, everything works fine. The difficult part was not to find this solution. The difficult part was to get the client running before it crashes. Had to be quick to rightcklick on the taskbar to pause sync. But it works fine now.
New problem, no related topics → create a new one! 
I moved your issue into a new topic.
It is a really interesting observation.
If you want to file a bug report, log files will be required:
https://docs.nextcloud.com/desktop/3.14/troubleshooting.html#obtaining-the-client-log-file
And you can submit one: