Earlier quoted context omitted.
In my experience, you couldn’t just setup an account and start selling, you had to contact their sales team and they let you know if they want your business. Stripe has no real competitor.
It has lots of competitors. They bought out LemonSqueezy exactly because it was a competitor that quickly gained a lot of mindshare. Polar.sh is another one. The thing you're talking about with Paddle is just checking you're not selling offline, physical stuff.
EDIT: Yup. Via their pricing page:
Polar is currently built on Stripe, and we cover their 2.9% + 30¢ fee from ours. However, they impose a few additional fees for certain transactions that we need to pass on.