take a look at the price development for this game here

https://www.gogdb.org/product/1850642020#prices

the 26 of Jan the pries was increased from 20 to 30 $
later the 5 feb that is 10 days later. The game went on sale for 24$. that is 4$ more that the previous normal of 20$
later on the price was toggled between 30 and 24 $ regularly, being at sale for 24$,
Right now it is at an all time low equal to the previous normal pricing of 20$

now i think that is kind of marketing is not legal in Denmark where i live.

Normally the normal price have to been there for at lest 30 day before a sale. Also the price has to be compared to the lowest within the last 30 days. In special cases for goods that become obsolete quickly 14 day is accepted.

Here is a resume of danish rules for marketing (written in the legal crap manor that I can't get head or tale off)
https://danskelove.dk/markedsf%C3%B8ringsloven

and here is a resume of the when the pricing is legal (written in a way i can interpret)
https://taenk.dk/raadgivning/markedsfoering/tilbud-hvornaar-er-prisen-i-butikken-og-paa-nettet-lovlig

goggle can translate this to English like so (hopefully precisely enough):
https://taenk-dk.translate.goog/raadgivning/markedsfoering/tilbud-hvornaar-er-prisen-i-butikken-og-paa-nettet-lovlig?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp

Sorry I can not link to some direct description of this made in English as these is danish lows.

Also I am not a layer so I can be wrong.

Would be insignificant as long as it's legal in Poland.

Don't misunderstand me, please, I like the rules of Denmark, but you're doing buisiness with a Polish shop in the internet, and therefore Polish law will be applied because the acceptance of this is included into the registration an this page.
There might be a small chance that a court will rate the local law as "more protecting" and therefore priorize, but I wouldn't bet on it...