The learn more button on the Floorp's Flathub links to a license agreement that literally states the following:

2.5. Floorp is not completely open-source same. Floorp's a part of codes are protected by copyright law and is not licensed under an open-source license. You may not use part of Floorp's code in your own projects without permission from the Licensor.

The file is 4 months old, so maybe something changed. Someone in the other comment linked a 1-month old Reddit post saying that Floorp is open-source again. But if that's the case, why haven't they updated the license agreement yet?

With Fairphone 5, they guarantee at least 8 years of software updates but they will actually try 10 years! ^1

And Apple was recently forced to disclose their software support commitment in the UK due to regulations. Apple guarantees at least 5 years of software updates, which is less than Google, Samsung, and Fairphone. Apple is no longer the leader in software support! ^2