Is Resident Evil 2 pay Monthly or just once?

I'm new to MacOS and I'd like to play Resident Evil 2 (available now on the App Store). BUT, when I launch the free trial it asks me to login to Game Center, Arcade, etc so it seems to me that Resi2 is actually part of Apple's Arcade thing which is a monthly fee. Not a one-off cost.

Am I wrong? If so, why does Apple make it so confusing?

If it matters, I doubt I'll buy it now as the sale will end before I get a reply, but new Mac users like me would prefer clarity when we are wary of getting tricked into Apple subscriptions.