shipped this since your comment: Settings → Import takes Pocket/Instapaper CSVs or any pasted list of links. for Vivaldi, open your bookmarks export and paste the contents, it picks up the URLs.
You might want to try Slax Reader – it saves full page snapshots for offline reading, and the content stays available even if the original link goes dead.
I was a heavy Pocket user. It shut down. So did Perch, and Artifact, all within a couple of years. They had one thing in common: simple, single-purpose apps for people who wanted to read, and that kind of app doesn't survive on its own.
So I built my own over a weekend, mostly so I'd stop losing the essays I meant to come back to. Clean reader, audio for walks, search, public collections. It's free. It's rough in places and things will break, but I'll keep fixing them.
Without a traditional login this is as user-hostile as a complete stranger’s wireless webcam mounted in your bedroom or bathroom.
I am liking what I am seeing, and will gladly use this once it has a traditional login + TOTP 2FA.