Four years later, I gave KDE Plasma another try... and boy am I impressed now!

Every single one of the issues I raised in my 2016 post has been fixed.

The display is butter smooth, and feels faster than Mint+Cinnamon (my previous distro+DE). Effects like Wobbly Windows don't even consume enough CPU to register much in KSysGuard.

Fonts look great on my 4K monitors.

1. Dual-monitor support is great (except for some applications keep opening windows on the secondary display, e.g. Firefox, which seems to be a GTK issue)

2. Discover still has a bunch of issues (I ran into 8 in a couple hours without even trying), but at least you can search for apps now.

3. The launcher now activates when you release the Meta key.

4. There's finally a sane and ergonomic Task Switcher - Thumbnail Grid.

5. Switching among windows with Meta+1..9 now works. This probably saves me half an hour a day.

6. Ctrl+Insert still doesn't copy text by default in Konsole, but it can be configured to do so.

7. The Bluetooth connection to my SONY WH-1000XM3 headphones is flawless.

8. Only cosmetic issues with the Audio settings window.

9. Bookmarks are still separate from Places, and I don't quite get why, but perhaps there's a good reason.

etc.

I'm very pleased with Plasma, and the more I explore it, the more I realize how insanely customizable, in practically useful ways, it is.

Like, seriously, why are GNOME, Cinnamon, Budgie etc. even trying?!
Plasma mops the floor with them.

(We could use their developer-hours to fix some of the annoying issues that Plasma still has, like the crippled locale format selection, which is a regression from Plasma 4).