Is it my imagination or Steam has taken its new beta UI to look like Gog 2.0 Beta UI?

No, that's just what today's standards and aesthetic trends are like.

if that's the case then it would be the other way around. steam leaked their visuals and working demo for new UI months ago, before galaxy 2.0 went to beta. I tried it back then and it already had same visuals and features.
Also if you'll check gog github activity you'll see they forked Playnite before galaxy 2.0
I can't confirm or decline the information if gog reused Playnite codebase for their galaxy 2.0 because it is closed code, but who knows. I wouldn't say gog has some kind of coding wizards to invent something revolutionary, their site is in very bad shape coding wise, old galaxy wasn't a prominent thing either so I would rather believe they resorted to forking and reusing someone's work. Valve on the other hand has experienced coders to deliver anything they need.

Like Ilona said, that is how current UI trends are today. You will notice a lot of clients look similar since it's a trend currently in design.

" I can't confirm or decline..." but I will post baseless allegations nonetheless.

Playnite is written in C#, Galaxy in C++ (at least the most part of it), so just copy and paste is a little pointless

and where is "allegations" in my post?

"gog reused Playnite codebase for their galaxy 2.0 because it is closed code, but who knows."

I made this statement based on the fact they forked Playnite. why they had to fork it?

I don't know, and you don't either - but I don't post such "information" accompanied by "I wouldn't say gog has some kind of coding wizards" or "site is in very bad shape coding wise"

Either you know something - then post it, or you don't know but then post nothing or at least without negative connotations

https://www.gog.com/work/software-development-lead-software-engineer-backend
https://www.gog.com/work/software-development-web-team-leader
https://www.gog.com/work/software-development-software-engineer-backend-php
https://www.gog.com/work/software-development-junior-software-engineer-backend-php
https://www.gog.com/work/software-development-software-engineer-frontend
https://www.gog.com/work/software-development-scrum-master

Could you be more on nose, please ?

I can stand by this claim. gog is awful in maintaining their site, their galaxy (1.2 up to this date), there was visual issues with site and galaxy layout after new site design and it took gog more than a week to fix simple issues that could be taken care of in 1-2 hours by the right coder. their galaxy 1.2 still lacks link to game store page (if it's a game from bundle - it have to point to bundle page but leads to nowhere). It had the link but it was removed with new site design and they still can't figure out how to add it back.

Both Origin and uPlay had that look long before Galaxy. It's just the current UI design aesthetic for gaming clients and GOG managed to adapt it brilliantly in 2.0.

It's remarkable, though, how clunky, ugly and outdated Valve managed to make it look despite so many role models. Oh well, at least they're consistent in their design philosophy of having Steam look like an early 2000s mishmash of UIs...

I actually think the older galaxy looks better. The dark UI looks drab and the shadows behind text looks ugly as well as the "see through" UI and the colors change each time.

The problem here is that you create a link between two observations you made (and can only speculate about the reasons for that) by mentioning them in the same paragraph > you create the idea that gogs devs aren't good so they most probably just copied work from others.