I’m an open source maintainer that asks for donations with a basic “Buy me a cup of coffee” link.

IMHO the person donating already got something in return which is the free software + the good feeling of having donated.

I don’t offer anything in return for a donation because I also don’t want those strings attached and I feel at that point it’s no longer a donation. If I offer something in return it turns into sponsoring or simply buying services/access.