WHERE ARE MY PAGES TEMPLATES???????

In System Preferences > Language & Region panel, is Swedish the topmost (Preferred) language, or is it English? If this is the case, would reversing these entries change Pages ability to locate all of your custom templates? Fishing expedition as I do not know how to solve this issue yet.

Interesting that it finds a newly created template, but no prior examples, even though present in that template location. In the Finder, compare the newly created template permissions with any of those that Pages is not finding?

Also, you might consider moving the individual templates that Pages does not see to a Desktop folder. Then open each one and save as a template, and see if Pages can now recognize them on creating a new document. That is what we say in the U.S. is a pain in the a.. or (PITA).

I have upgraded two Macs here from Mojave to Big Sur 11.1, and installed Pages v10.3.5 at that time. Pages was subsequently updated from 10.3.5 to 10.3.9. When I launch Pages, on either Mac, it presents the template chooser and all of my templates are present.

What you have encountered is unique, and I have no prior experience other than the Preferences panel suggestion on how to resolve it. You can reboot your Mac into Safe Boot mode by holding the shift key immediately on the reboot, and until you see a customary progress bar. This will be slower than normal as some additional system processes are running.

Once you have signed into your user account, launch Pages again, and see if the template chooser appears. If it does, then reboot normally, and check again if a launch of Pages continues to display the template chooser. If it displays in Safe Boot mode, and not in a normal boot, then that raises the question of application interference such as running an anti-virus application, or something that may have damaged the Pages application.

I find it strange that in your path, that Bibliotek replaces the customary Library container, but the second reference to Library in that path is unchanged. The path to my Pages v10.3.* templates:

~/Library/Containers/com.apple.iWork.Pages/Data/Library/Application Support/User Templates

If you renamed ~/Library to ~/Bibliotek, I recommend that you change it back ~/Library. I do not have any non-English installations of macOS here to determine if those use local dialect names for these folders.

Have you looked in that User Templates folder to see if your other custom templates are there? If not, you could restore them from a Time Machine backup prior to the date they went missing.

In your Pages Preferences > General panel, do you have Show Template Chooser selected?

Does the template chooser not show when you select File menu > New…?

You are welcome. Baffling too. Back to work now… 😎