Can you give an example?

The stupid issue for me is, that when you do a Keyword Search and hit Enter, it goes to the first hit directly, instead of the list.

For example: Type "Kingdom" into the search bar, and hit enter. I am taken to the shop page for Kingdom Come: Deliverance...
To get to the results page, i need to scroll to the bottom of the list (that shows mostly Kingdom Come Deliverance DLCs and variants) and click "Show all Results".

You don't have to deal with that if you do your search on this page https://www.gog.com/games?page=1&sort=popularity

I've found an example

Vampire®: The Masquerade - Bloodlines™

The search page mentioned above fails to return results if you don't include the ® symbol when searching for multiple words starting with Vampire.

A search of the form

Vampire | The Masquerade

will pick up the game in question. The | symbol acts as an OR symbol, so "Vampire | The" is decidedly unhelpful.

Curiously enough, the search option in the top toolbar behaves differently - it picks up the game without a problem.

Where are you searching in? Is it the same as in the attached photo?

Yes, but now it is showing. I'm confused, and perhaps a little blind.

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I have had this happen once or twice over 10 years with steam but with GoG I have had it happen quite a lot. When there's a game I fancy I check with GoG first, search comes back negative so I buy it on steam. More than a few times I have found the game on GoG by doing a search for answers on that game, comes back with a GoG link, or mentions the GoG version in some way. Sure enough the game was on GoG all along. It is as if the game has not been entered into the library of games.

It's not easy to discover as you trust the search result was correct and walk away.

I'm picturing little gremlins running around inside the web server, disconnecting/reconnecting links, bashing handshake protocols, flushing memory caches, etc. Then there's the head gremlin doing an imitation of the Soup Nazi from Seinfeld.

No results for you!

Okay. I'm going back to sipping my rum. Bye-bye now. Later then.

Same experience as Amund and Mortius1. Tne search engine at (click) "Store > Browse all games" is more reliable. E. g. if you want to see say all xcom games, that's where to look for. Otherwise you end up with Ranayna's mentioned problem. The search option in the top toolbar is kinda wibbly.
I agree with OP, they should fix it since it's the first search option presented to the customer. Wibbly search = lost sales.