So I go to this Adrenaline sale and none of the games I have are marked as in library, like it used to. It was bad enough the oldschool view of sales is gone, where the whole game was grayed out if you owned it, so I can spot it easy.
GOG sales UI getting worse and worse.

It's a bug. Has been around for a while. GOG Is "aware" and doing something or other. They decided against making any sort of well visible statement about it, however, so you're the 487th person to make a thread about it. Your bad luck - if you'd have waited just a bit more and been 500th, you'd win a year's supply of purple dots.

GOG Galaxy is unaffected by this site bug.

Apparently Galaxy is unnafected but I do not suffer the glitch on the web site either. And I tried hard to force the bug. Where I do experience intermitently that glitch/bug is when I browse the site using my smartphone. At least the non present "In my Library" or "wishlisted" labels part.

Instead of:
https://www.gog.com/en/promo/20231019_adrenaline_rush

try:
https://embed.gog.com/en/promo/20231019_adrenaline_rush (replace the "www" with "embed")

followed by pressing [CTRL] + [F5]

It's a workaround by GOG user Palestine, and it works.