Right, I remember now. The file extensions weren't correct, but even after renaming the files it does not work because the imports were also missing the correct file extension (which is mandatory in ESM mode in Node.JS). At that point I gave up.
Is there a good android app for librephotos (or any other application) that offers similar features than Google Photos? A while ago I tried adding photos to my nextcloud instance, but the nextcloud app in my opinion is very rudimentary. I really missed face grouping, location search, the year based scrollbar, etc.