How to add many notification sounds or ringtones in one go?

I downloaded an archive with a bunch of notification sounds (the ones from Cyanogenmod which I’d like to keep on my new Pixel 5). Unfortunately just putting them in the Notifications folder didn’t work. They do not show up under “My sounds”.

I can of course add them one by one, but for obvious reasons that’s not an option when there are about 100 sounds I’d like to add…

Is there any way to bulk-import the sounds? I expected putting them in the folder to be enough, but apparently that’s not the case?!