How can I hide or turn this panel off?
Thank you.

You can't.

By using a dedicated browser for your browsing needs.

I think GOG Galaxy has many things to improve.

There's a whole new Galaxy to discover.


Ok, that was bad... leaves

HAHAHA

If they haven't yet they should make the new Galaxy allow one to hide/shrink that panel.

Grab the window, move it left until the panel is out of sight, profit.

Given that it is integral to the entire purpose of Galaxy, why would you want to? It's a list of your installed games. Why would you use Galaxy if not to install or launch games? New Galaxy doesn't have that panel, or rather the panel that's there has a completely different function.

1st bit: Maybe they want to hide it when not using it to be able to have more screen real estate for the main window?

2nd bit: Can you shrink or hide it, though? I mean a simple tab that shows when it is hidden to open it back up would be nice, I would think.

In both cases, I'm not sure what you'd need the extra space for? If it doesn't impede you installing and launching the game you want to play then I'm not sure what advantage there is to being able to hide it.

Some people either might want as much space as possible for the main screen/window, or they might be a bit "autistic"(no insult intended) about it and just want to keep their screen free of "clutter".

Heck, some people like to go minimal/no hud in many games for the same or similar reasons.

Tried using this marvellous tool called... a browser?

It's a closed beta, you have to receive an email invitation from GOG first to be able to download and use 2.0. And because they're sending invitations to people who signed up for beta first, you're at the very end of the queue I'd imagine. My guess is that the closed beta ends before you receive your invitation. ;)