Please tell me why mice is visiting my garden when I have a fully grown enchanted mushroom growing?

They don't deter 100% so some mice are inevitable, whatever your setup.  But you need your snowdrop to be fully grown to get Snow White and the Queen, so all your apple can attract is mice.

Although your enchanted baby mushroom is fully grown, it will only partially deter mice. Only a fully grown supershroom fully deters (though a pest might be programmed in before the shroom is fully grown).

I see someone has spotted your 45th Snow White and has planted the snowdrop for you.

Snow White is only average, but field mice are very common

It must have been fully grown... hasn't recently been dusted and is at 66%. FG is at 60%

Thanks for all the replies. I've done all the previous with a SS, but had to pull it everytime to get Snow White. My enchanted baby mushroom was fully grown, since a few hours. I've dusted it before all the mice showed up, but okay I understand that you still get some mice. (Such a long time since I used another mushroom instread of the SS)

It's also not correct that I need a flowering Snowdrop for Snow White or the Evil Queen, only the apple. When I'm ready for my next dwarf, I do need the flowering snowdrop, so will dust it then.