Earlier quoted context omitted.
This is a feature of iOS safari with the read later list. It‘s not been particularly reliable for me though.
iOS's implementation is definitely useful, but I was thinking more along the lines of a permanent archive persistently stored. iOS seems to optimize for temporary offline scenarios; saved pages do not seem to be backed up or synced to iCloud.
The best bookmarking option for archival seems to be the pinboard.in archive plan.