Growkits are 100% legal in Poland
You can legally buy them in the store MushLove.pl and legally store them.
You can conduct research under a microscope or simple observations.
You can keep growkits at home without any problems.
Note - while growkits are one hundred percent legal in Poland, you are not allowed to make the mushroom itself, i.e. the so-called fruiting body
Psilocybe Cubensis mushroom fruiting bodies contain substances that are banned in Poland.
To avoid trouble, do not make fruiting bodies from mycelium and, just in case, pour fungicide over the growkit within 72 hours of receiving it so as not to break the law currently in force in Poland