No. Jonathan was co-maintaining KDE neon, which now has one developer left and is about to be joined by KDE Linux, another take on a Plasma-based distro. He also handled release manager duties, which have been transferred and running smoothly for a few months now.

He may have contributed in other ways that I'm not aware of, but overall KDE is in a very good spot with many more developers working on stuff.

For others who might not know, KDE Neon is a distribution. I was initially confused because I thought it might have been an alternative desktop environment to KDE Plasma.

This is probably the greatest curse and blessing of modern Linux: there are an impractical number of distributions. I guess you could probably say the same thing for desktop environments, various services, bootloaders, etc.