I just installed Kubuntu last week so I could get the additional shift-drag targets to split my 34" ultrawide into 3 sections, or bump to the edges for the half filled.

Install i3wm, it will change your life.

Something I realized after spending a few months in sway (i3) and then niri is that I only care about a few windows (code editor, terminal, browser, apps I use moment to moment).

All the rest I'd prefer to just summon as-needed and then dismiss without navigating away from the windows I care about.

sway/niri want me to tile every window into some top-level spot.

Took me a while to admit it, but the usual Windows/macOS/DE "stacking" method is what I want + a few hotkeys to arrange the few windows I care about.

Yeah, I came to the same conclusion a few months back. Sadly I had to ditch KDE for GNOME due to an issue[0] specific to NixOS but after going through the gauntlet of tiling window managers and PaperWM/Niri over the years I've also settled on a traditional DE.

[0]: https://github.com/NixOS/nixpkgs/issues/126590

I'm surprised to hear that niri didn't work for you, I feel like it's a really good middle ground between tiling and floating window managers. It handles a lot of window resizing and arranging for me, without being too rigid. Windows can have any width they need without having to evenly divide my monitor.

In sway, put the lower priority windows in another workspace, or the scratchpad, or in tabs/stacks. You can bind keys to focus specific programs by their appid/class also, so even if they're on another workspace or monitor it'll jump right there.

It sounds like the scratchpad may be especially close to what you want.

Maybe awesome-wm would be better for you then.

I’m currently using Krohnkite [1] to get dynamic tiling in KDE, and Klassy [2] to get i3wm-like pixel borders instead of full window decorations.

[1]: https://github.com/esjeon/krohnkite [2]: https://github.com/paulmcauley/klassy