The best option, though not without issues – Pins for Pinboard Review

This is hands down the best cross-platform Pinboard client availabe right now for Apple devices. It's modern, actively maintained, and works well -- most of the time. My biggest gripe with the app is that the Share menu action can occasionally lock up the entire browser. The "Cancel" button will not close the window. I've seen this most often on macOS. The only solution, as far as I know, is to quit Safari entirely. For an app that revolves around saving webpages, this is a big problem.
Review by alechemy on Pins for Pinboard.