Apartments and houses are designed for air flow. You don’t need a gap in your door to prevent mold. Mold will grow despite that if you live in a city that has high humidity.

Everyone should watch for mold. Check around windows. Behind the toilet tank. Above and around the shower. Wipe with bleach often.

You can also get a dehumidifier if it becomes a problem

QP still puts you with similar skill level players. It just doesn’t show you the algorithm like competitive. You won’t be put with a diamond if you are bronze and vice-versa.