Personal experience - I used some late version of Plasma 5.2x on desktop and now Plasma 6.x of course (always Wayland, generally always the latest stable version available), and Gnome (always Wayland, always the latest stable version) on my work notebook. I’ve never experienced any “serious” bug on Gnome, but I have experienced multiple on Plasma over that time period. I think the most “serious” bug I’ve had on Gnome was that the cursor was flipped upside down for a while until they fixed that (some time ago). While the most serious bug in KDE were multiple crashes in plasmashell since Plasma 6.x. (Meaning all your open apps got closed, I’d say that’s pretty serious for a bug). Another smaller bug, very recently, was that virtual desktops in KDE Plasma were named wrong and when I renamed them they didn’t get saved so it reverts to the wrong names (e.g. “Desktop 1”, “Desktop 3”, “Desktop 4”, “Desktop 4”). But it seems they fixed that with the latest update as well.
Which is also why I’d like to keep it that way, Gnome for work and KDE where it’s not super important if plasmashell crashes or does some weird thing every once in a while. I think KDE is more prone to bugs because it’s simply more complex than Gnome. Gnome is quite minimalistic and doesn’t offer lots of features, KDE is a powerhouse desktop with literally tons of features, dwarfing probably every other desktop environment, at least in the available options for which a GUI exists to set them. Also, Gnome doesn’t support many advanced features like HDR (yet), while Plasma does. So the complexity in having all that stuff means Plasma must be more prone to bugs.
So I view KDE Plasma as “slightly more buggy” than Gnome, still. Especially for dot-zero releases. But the KDE devs are also improving it all the time, so it might become more stable soon. But still, for personal use, KDE Plasma is “stable enough” despite those mentioned bugs, some of which were also fixed in the meantime. For example I didn’t have any more plasmashell crashes since they said that they fixed those causes. Which is why I’m using KDE Plasma 6.x for my personal machines. I like it more than Gnome, but when I want “100%” reliability for a DE, I’m still using Gnome. The main thing I dislike about Gnome isn’t actually its UI or design philosophy or even the limited GUI-based options it offers, but rather its philosophy regarding standards or compliance or making interoperability easier. The Gnome devs often do their own thing and don’t play that nice with others.
Gnome on my work notebook, KDE Plasma on my own machines.
I like KDE Plasma better overall but Gnome was a little bit more stable for me so far. I don’t mind UI differences that much, I’m not very much reliant on the GUI and can deal with pretty much any UI paradigm.