On donations, it's kind of ridiculous that the PayPal mobile checkout doesn't support 2FA:
Your Security Key can't be used to log in here. But, you can still complete your purchase with PayPal by checking out on your computer.
It also looks like it was designed in 2004 and never touched again. This same issue affects the Cydia store, and the only workaround there is to disable 2FA.
I've given a donation in the past - and anyone else interested can see the big donate button on the site.