Most software allows it because they run in Docker. But AFAIK, you will definitely not violate any license, if including an app like BTCPay in Umbrel would be forbidden, it would be Umbrel's responsibility, not yours.

Umbrel said in June 2022 that they are not prohibiting running shops, but I'm not sure about now, because they only recently (and secretly) introduced these TOS, which try to restrict what you can do with your node. Even saying "Don't do illegal stuff" restricts your freedom to do so, and it seems to apply US laws everywhere (Not a lawyer, so I may be misunderstanding point 11).

Also dangerous is ". You may not reverse engineer, decompile, or disassemble the software, except as permitted by applicable law. " -> Umbrel sometimes keeps code closed source after releases for some time, and this essentially forbids anyone from trying to figure out what it does in such a case.

Disclaimer: I develop a noncommercial FOSS umbrel alternative at https://runcitadel.space that will launch soon, which also includes features like HTTPS to make running shops easier.

Point 7. Restrictions on Use. It prohibits commercial use, and running a shop seems to be commercial use.