Thanks to the suggestion of @tal, I'm now a happy Pinboard user for at least the next two years. Only thing which made it tough for me to use Pinboard is that it is not easy to find a good mobile app and a good extension for Safari.
I'm now using Pinstachio on my iPhone and on my MacBook. I can use it in Safari via the share sheet, but I would have liked it to have it like an extension.
A perfect solution for me would be something like the Zotero extension. Just one click and all the important metadata and the link will be saved in Pinboard + a good and easy to use UI.
But for now, I'm happy with what I have now. Maybe someone can recommend some nice tools for using #Pinboard.