I was a previous Pinboard customer. I've since moved to Linkding[0], a self-hosted solution, and highly recommend it. It's got the same feature parity as Pinboard but gives me much more confidence about the longevity of my bookmarks.
Internally, perhaps, but it doesn't have external feature parity when it comes to, e.g., being able to automagically import things using IFTTT.
(Yes, I could probably lash up a webhook feeding into linkding but IFTTT's webhook support still isn't great but I'm already 20 projects behind on my personal list and redoing all my IFTTT recipes that talk to Pinboard isn't going to be a priority.)
Linkding is definitely worth a look though as backup.
0. https://github.com/sissbruecker/linkding