I used both LibreWolf from a Windows 10 computer and Brave from a Linux device yet both experienced code replacers (black diamonds with ? in them) when first entering the homepage then after a refresh both also experienced Error code: 503 Service Unavailable at the checkout page. Is this happening to anyone else? It has been this way for atleast 5 hours now.

I'm the same as you, first it wouldn't accept my card, several times and nothing, then I would get errors or the page would come up with the little man holding the terminal symbol (or so I suppose, it was a globe) every time I tried to go to the payment page, then it started doing that in settings too and sometimes it would show that I still had my purchases in the cart...

Sounds very familiar. I think there are quite a few problems at the moment, this post or example, it tripled up. I admit I clicked the post button three times, but it didn't give me any feedback to say I have clicked it. Something is quite wrong with the site right now.

I think it's site wide, me and some others can't get into the account / game section part of the website of purchased games to actually download them. Might be due to the sale happening (does happen ever so often when big things/sales happen)

Yeah same here, I can’t access my game library, instead I get the page with a little bear holding the whole earth on its shoulders…

This lone being bears the heaviest of burdens. Its kin had abandoned it, utterly, leaving it to face the challenges of life, without the benefits associated with inherited generational wisdom. Circumstances have dictated that it must accept responsibility for the mistakes of the elders, while enduring such unbearable hardship. As it tirelessly strives to find its bearings, in a world composed of chaos, it can but only muster the strength to dream for a better tomorrow.

GOG is currently being inundated by a gigantic flood of user traffic (due to the current Back to School sale). If you were to return later tonight (in France), the problems might be resolved. Otherwise, as GOG staff adapts accordingly (and/or traffic subsides), it would be best to wait until the morning (at the very least).