I’m using MacBook Pro with latest version of MacOS.
I always update Postman to the latest version.
My largest collection has a few dozen requests, and I have about 10 collections.
I only use Postman for manual testing, 1 request at a time, so nothing is running in the background.
I restarted Postman and this fixed the problem, but I noticed that it is gradually becoming slower over time, so you might have some kind of processing leak.