I've used *nix extensively headless for the last 30 years, but I have decision paralysis when it comes to figuring out what the heck Linux distro is good for a desktop.

Just go for whatever DE looks pretty to you, I personally like KDE. Don't be afraid to switch to a different desktop later on, its just a few packages to install most of the time.

As for distros, pick something established that looks good to you. You said you have experience, so you probably know what you want from a distro. I ran arch on my machine a lot but recently switched to fedora for its simpler installation.

There's a handful of the easy ones, all offering slightly different experiences, all good.

Ideally you'd spend at least a day or so trying them all, and about a week reading and watching about their differences, pros and cons.

Unless you are using nVidia for gaming or have an obscure hardware configuration, chances are you're supported wonderfully well at this very moment, by at least 2-3 distributions (Mint, Manjaro, Fedora, Ubuntu, Bazzite, SteamOS, PopOS, CachyOS -- you'll also have a choice KDE/Gnome).

All you need is pendrive. For the super easy transition you'd want an entirely separate system drive (nvme for example). I know, its expensive. I said for the super easy transition, its not necessary. Slow portable disk to store your current documents and game saves should be enough.

We live in the exciting times.

Honestly, pick one of the well known distros at random. Personally I use Manjaro with GNOME: up to date software and a polished out of the box experience. I never have to go to the terminal unless I want to.