There's no paywall, it just asks you to pay for the software. You can use it without paying for as long as you like, but it's paid software. See: WinRAR
It's not a donation, you're expected to pay for it. Donations can be of any size, this is a $10 one time payment for the use of the software. There's a license key and everything.
1. not open source.
2. has pay-to unlock feature but no idea what is behind the paywall. the website doesn't mention having to pay for it
3. does not have sponsorblock or anything related to that in the settings
edit: i don't care about "OSI compliant is only open source", rather i am fine with any free license