At the moment, filters for "The recipient" include emails other than the destination for the email.
Eg: say I want to apply the label "not-proton" to emails received because they have been forwarded from an outlook or gmail address.
Using "The recipient" it is not possible to distinguish between OTHER recipients of the email and the one that caused the email to be received.
Say my proton is example999@proton.me, and I have gmail addresses example001@gmail.com through example999@gmail.com (so impractical and annoying to specify all 999 of them but you don't want to also catch example1000@gmail.com because that's not you)
If I use "The recipient" matches "*@gmail.com" the filter will catch it even if it was sent to someone else's gmail eg: "To:" is "example999@proton.me, notme@gmail.com"

I can and am using sieve filters to do this, but it seems ridiculous for the average user to need to use what is called an advanced feature.