@mcc I think I've read all the side threads here. Your journey's are always interesting to follow for me. Please *DO* enjoy some time just using the computer! Disclaimer: my setup is mostly Wayland due to refresh rates being better for my projector, which tends to angle me towards more recent distro releases.
Congrats on ditching snaps! Was the idea to go to Debian that it was stable/familiar to Ubuntu? Maybe I'm in the minority, but Debian stable is just too old for what you seem to want to do. Are non-LTS Ubuntu or Fedora's upgrade cycles too frequent for your workflow? Either would give you more recent versions of both DEs, and Fedora would give you more "vanilla" GNOME than Ubuntu would.
The ‘x11-randr-fractional-scaling' flag all seems from ~2ish yrs ago posts that I see, but I can't tell if this is needed in GNOME 47+ which is what you'd see in non-LTS Ubuntu or Fedora. GNOME 47 finally seems to fix the chromium/electron/x11 fuzzy rendering in Wayland, so I may give it another go. Fedora is very Wayland forward if that's a problem for the Quartus IDE you mentioned (seems like java from the Arch Wiki, which makes me think it'd be fine for Wayland).
I can understand you giving up on KDE, especially the Plasma 5 that would be in Debian 12, and coming from GNOME/Cinnamon's simplicity. It is possible to make it less ugly! My .02 would be for you to try either GNOME or Plasma 6 versions of Fedora (even the live environments) and see if you get more of the “it just works" feel. Still should have wide software compatibility to install what you need like Ubuntu/Debian. I think you ask more of your environment than I do, as I only do light programming these days and play games through Proton.
I’ve personally been thinking about some atomic spins of Fedora being great for recoverability, but 1Password is a part of my workflow and it just behaves oddly on those setups. The ability to instantly rollback might appeal to you in Silverblue, and it's heavy Flatpak focused to boot.