In general, the people who have 2nd vacation homes buy single family houses or condominium apartments. They don't rent, because that doesn't get them ownership of anything. The 2nd home is generally a more speculative investment than anything else.

So no, they're not really pushing up the costs of rental apartments, because they're not in that market segment at all.

Meh. It's the software engineers making $150,000 each bidding up the cost of apartments more than it is J Random Tourist-Supplemented Income dude.

I have no idea if AirBnB does that to apartment rents but I do know that some formerly sleepy coastal towns became too expensive (in recent decades) for locals to buy a house due to second homes being bought there by wealthy non-residents. I have no idea how to fix such a problem but I know it is real.