Where can I set the user timezone?

Nextcloud version (eg, 20.0.5): 28.0.3
Operating system and version (eg, Ubuntu 20.04): Archlinux running community docker container
Apache or nginx version (eg, Apache 2.4.25): Reverse proxy in Arch 2.4.58 plus Apache in container
PHP version (eg, 7.4): 8.2.16

The issue you are facing:

Sorry, this question might be dump but where can a user set his/her time zone?

I found the setting in the oc_preferences table with appid='core', configkey='timezone and the appropriate userid. But this involved access to the DB by the admin and cannot be the way to go to change the personal time zone.

I stumbled over this as a user was not receiving any emails but instead, the activity app spammed the logs about the inability to get a valid time zone for said user. It was set to Etc/Unknown which is obviously no valid time zone.

I saw that other users as well do have a wrong time zone setting but at least a valid time zone. So here it is merely a question of usability.

I skipped over all logs as this is a pure UI/UX issue.

Normally I think it is done from the browser, you can disable the detection from the browser (in case of FF):

You can set a default time zone if most of your users are in the same one:

Then in theory, I’d expect that it should fall back to this one…

Oh, sorry, I missed the notification.

You mean the someone of the browser at the time of initial login? Or is it the last login that counts?

My problem is not the frontend to show e.g. the creation time for files. Instead, there is a bad entry in the database that prevents the backend to send mail notifications.

As a workaround, I changed the debrief in the database directly to valid values to get the notifications running. But I do not understand the reason it was set wrong and how to fix it without DB access.