Yeah, same with Apple Card. Need to have a iPhone as they can’t make a website to view your statements and pay like 99.99% of credit cards have. So if you want to maintain that account and switch to another platform like Android that could be tricky. Or if you lose your iPhone however I think calling support might work but not sure how they’d handle payments without your iPhone.
Also if you sign with iPhone, and want to switch phones I’d hope the developer would have a way to set a username or email and password on your account or link another account. So you could have Facebook and Apple linked to the same account, unlink, etc.