Nextcloud version (eg, 20.0.5): 25.0.9.2 → 26.0.4.2
Operating system and version (eg, Ubuntu 20.04): Docker image: production-fpm (currently 26.0.4.2)
Apache or nginx version (eg, Apache 2.4.25): Docker image: nginx:mainline (currently 1.25.1)
PHP version (eg, 7.4): Nextcloud docker image: php:8.1-fpm-bullseye → php:8.2-fpm-bookworm
The issue you are facing:
When I pulled a new version of the production-fpm docker image, it will no longer start up. It errors out complaining…
nextcloud_1| Can't start Nextcloud because the version of the data (
nextcloud_1| Warning: PHP Startup: Unable to load dynamic library 'imap.so' (tried: /usr/local/lib/php/extensions/no-debug-non-zts-20220829/imap.so (libc-client.so.2007e: cannot open shared object file: No such file or directory), /usr/local/lib/php/extensions/no-debug-non-zts-20220829/imap.so.so (/usr/local/lib/php/extensions/no-debug-non-zts-20220829/imap.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
nextcloud_1| 25.0.9.2) is higher than the docker image version (
nextcloud_1| Warning: PHP Startup: Unable to load dynamic library 'imap.so' (tried: /usr/local/lib/php/extensions/no-debug-non-zts-20220829/imap.so (libc-client.so.2007e: cannot open shared object file: No such file or directory), /usr/local/lib/php/extensions/no-debug-non-zts-20220829/imap.so.so (/usr/local/lib/php/extensions/no-debug-non-zts-20220829/imap.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
nextcloud_1| 26.0.4.2) and downgrading is not supported. Are you sure you have pulled the newest image version?
So for some reason Nextcloud is thinking that 25.0.9.2 is a higher version number than 26.0.4.2. 
If I switch back to using the 25-fpm docker image, it starts up just fine with no such errors.