You may be out of luck for now. https://github.com/sddm/sddm/issues/1399

There is a section here on dual booting using systemd boot. Never used it, but it will hopefully work in your case, or at least point you the right way.https://ostechnix.com/dual-boot-windows-and-pop-os/

Bodhi Linux. Lightweight and beautiful

I have never used those tools, I usually just dd the iso to a usb. I am assuming you are on a linux distribution already. I would download a fresh iso and verify the checksum. Then use dd to write to the usb. I use this format, and of course replace the path to iso bit and /dev/sdx (your usb)with what is relevant to your situation. Just open terminal and type

sudo dd bs=4M if=path/to/your.iso of=/dev/sdx conv=fsync oflag=direct status=progress

You probably already know but you can find the usb’s specific /dev/sdx with sudo fdisk -l

You want bleeding edge but are moving to Ubuntu 20.04, which was released in 2019 with a 2025 EOL? No DE from that release’s repo will be bleeding edge. You can manually install the newest releases of software you want, but that’s not really a “just works” solution either. You’ll run into dependency hell at some point. I’m not really sure what you’re going for. But as far as a stable DE goes, and if that is the main concern as implied in the title, XFCE has been pretty darn solid for me.

Have you tried turning off the repeat keys function? https://help.gnome.org/users/gnome-help/stable/keyboard-repeat-keys.html.en