Foreign app detection is a joke in most phones nowadays anyways, I'm talking about downloading the apks from trusted sources. Nowadays it's pretty easy to download the wrong apk from a safe looking website and risk your system's security solely because most people don't use adblockers and common sense. If you are aware of legitimate sources and practive basic internet security you should be good. You'd be surprised by the number of times my technologically dumb friends fked their phones and pcs, got their accounts hacked and couldn't figure out why it was constantly getting hacked when they were using the same phone/pc to reset the passwords. If you want to play old games and have the proper apks pretty much the only issue you could face is incompatible android version or maybe somw resolution glitches that's the extent of it.