I am having exactly the same problem, but with the v2.36.3~ynh2 version and trying to update to the v2.36.3~ynh3 version!
The update process trouble starts with “php8.3-gmagick : Conflicts: php-imagick”, then the same dependencies cannot be installed.
I am in trouble on my side, because now trying to launch SnappyMail, either on user or admin mode, is getting me only to a “403 Forbidden” nginx error 
Anyone has an idea to help?
I would gladly try to uninstall and reinstall the app, but will it erase all my settings in the process or will my data be kept?
[UPDATE] Nevermind, I found a working fix here: [Snappymail] Unable to upgrade
As advised by @adlmr (a big thanks to him!), I typed the following instructions:
apt-get remove php-gmagick php-imagick
apt-get update
apt-get install php8.3-imagick
And then, the update went flawlessly, and SnappyMail was working normally 