Thank you...I'm trying!! It turns out there's some distribution publisher stuff going on, that I have to sort out first. I've kept the old demo up for now at least.
I also looked into GOG but apparently it's invite-only now?
You can submit your game at https://lp.gog.com/submit-your-game/en. they will eventually check it and invite you to the developer portal.
Once you have access to the portal, you can use their CLI tool called Pipeline Builder.