Not a KDE dev, and I don’t know what’s up with the “Get New” screens not loading correctly, but for what it’s worth…the version Nate was referring to as ancient was Plasma 5.24.7, which is over two years old at this point. Plasma 5.27 is also “old” at this point too, though, simply in that it’s no longer generally being worked on by KDE developers.
Distributions like Debian, openSUSE Leap, etc. view it as a feature, not a defect, that they do not keep up with upstream development: DontBreakDebian - Debian Wiki
In that model, any bug fixes, security patches, etc. then usually become the responsibility of the packaging team for that distribution, since they are often intentionally not adopting upstream version updates even when they are for bugfix purposes (ex. KDE Plasma 5.27 had six additional bugfix releases after 5.27.5, up to 5.27.11, none of which were packaged by Debian).
Again, I don’t know about this specific issue, but on the general topic of “Why isn’t Debian/etc. on Plasma 6”, I figured that might be helpful context.