Hello, recently I came across this in my local shop. Does anyone know if it's a bootleg? Or some official merchandise, because I can't find anything about it on the internet.

Oh wow, would you mind sharing where you've seen it?

I found it at a Polish second hand market.

Some years ago, GOG sold merch.
Maybe this is one of those items.

Wow, it is very cool, but they forgot the . of the gog.com.

Look what I found.
I wonder how many people...

It looks like its from their 10year anniversary

I know some people who would happily buy this XD

I haven't checked it yet, I'll try to find something about it. Thank you :)

Oh, so I guess they only had the one pin, not a bunch of them?

Unfortunately, I found only one.

This is the kind of merch / promo materials often done as a bonus on giveaways / in goodie bags for conferences and generally as a company like this you'd have some about for visitors etc.

Given you're in Poland it could be as simple as;
Random person (GOG customer) turns up at GOG offices, meets staff, they're nice and give a little goodie bag. Person goes home. Doesn't want the pin badge / decides they don't like GOG. Badge goes in shop.

EDIT:
I work in gamedev and gamedev events (sometimes I find stuff like this from an event or project I worked on in a shop).

Ouch! Ten years here and now i see that, you are right. xD

Yeah I have a couple of those too. As digital versions, not physical.