have a backup and skip the do-release-upgrade script, edit /etc/apt/sources.list directly for newer repos, outcomment anything 3rdparty (in sources.list.d/ too)

have a backup and skip the do-release-upgrade script, edit /etc/apt/sources.list directly for newer repos, outcomment anything 3rdparty (in sources.list.d/ too) and update+upgrade+dist-upgrade your system into the future, did it this way for years.. it's almost a rolling rhino