A thing I've been wondering, I might be completely lost in thinking about this, but do you know: If you grow mushrooms at home is there a risk that it spreads as kind of fungi to the building, furniture etc.?

I agree with the replies so far in that there isn't a major risk of the mushrooms spreading.

That said, it's not completely risk free and I think it's important for folks who decide to get into the hobby at least take a moment to think about it. If you have someone in the household that has respiratory issues, I think it would be worthwhile ensuring that you have good containment to prevent spores from circulating the home (or do it elsewhere). This is particularly true if you decide to scale up (which is natural once you have some success, it truly is fun).

Also the growing environment is subject to infection from whatever environmental molds/fungus/etc are around, so reasonable precautions should be taken when handling/disposing. Once you get your procedures down this is less of an issue but still something to keep in mind.

Personally I didn't do anything but very basic precautions and never had an issue.

Mushrooms are everywhere. There used to be a subreddit of "weird mushrooms" like growing out of people's couches or in the bathroom, etc. In all cases, this is a sign of rot due to water intrusion.

You can grow mushrooms at home, it is fun. The only risk is that the mushrooms with high spore production are not great to have in a closed residence, especially oyster mushrooms which produce very high spore loads. There are vendors who produce cultures of sporeless oyster which can be used to grow oyster mushrooms indoors.

Outdoors, at least in most temperate areas, you are limited to things like shitake on logs or winecaps. The latter are incredibly easy to grow, and very good taste wise, but they are temperamental and basically grow on their own schedule, infrequently.

Normally the risk of airborne spores taking over your growing material is much more likely than your (most of the time very selected and in no way adapted to the "normal" surroundings you try to grow them in) taking over your home. Keep in mind that almost all fungi like similar conditions and there are already loads of spores of fungi that are more adapted to your living conditions in the air.

Nope. Edible mushrooms generally need similar conditions as mold/mildew/rot to grow, i.e. moisture, low light, and the right material -- though they tend to be pickier, and are less suited to human-adjacent conditions. So if you find mushrooms growing where they shouldn't, there's a much deeper moisture and mold issue.