The newest updates fixed this issue for me and I no longer get the message about outdated runtimes.
- Plex Desktop has been fixed yesterday (GitHub - Pull request)
- Plex HTPC has been fixed a few hours ago (GitHub - Pull request)
As statet in this comment, this may also fix certain hardware acceleration (compatibility) issues.
However, PlexAmp hasn’t been fixed yet. The pull request is still marked as open (GitHub - Pull request)