I encounter a couple of issues updating from Seafile 10 to 11 (Community Edition).
The first was getting a CSRF error using the web GUI. The solution to this is in the Server manual at seahub_settings.py - Seafile Admin Manual - it appears to be related to that latest versions of django being more fussy about this. However, I think this need to be included in the upgrade notes (Upgrade notes for 11.0.x - Seafile Admin Manual)
The second is that the captcha image is broken. From some investigation based on the logs, it appears that the Pillow 10 library no longer supports FreeTypeFont.getSize (see 10.0.0 - Pillow (PIL Fork) 10.2.0 documentation) - but the captcha image handling code tries to call this causing an exception.
A simple work-around is to switch back to pillow 9.* - however, as Seafile 11 explicitly includes pillow 10.0.* in its setup instructions (both for initial install and upgrade), I don’t know if using Pillow 9.* breaks something else.
I also had some warnings about sql errors during the upgrade script - but afaict it worked despite this.
Matthew