There isn't a way to cancel or delete a payment once it's been recorded, and that applies to all forms of payment in Square including the "other" option. It's intended to prevent fraud, as bad actors could otherwise delete payments and hide transaction records. I'm not sure if it's a regulation or industry practice (I know Quickbooks does the same thing), though it would be nice if there was a 5 second window where a payment could be canceled; I've accidentally hit the wrong tender button a few times.
I recommend that you make a note to ignore the payment when you do your 2022 taxes as otherwise you might report it as income instead of a donation. If it were me I would put it in my folder of stuff for my tax preparer.
What I do when donating is to type up a receipt in a Word document because there's no way to create a donation receipt in Square. I once created a Square invoice, printed a few copies, then canceled it, but it was cumbersome. This isn't unique to Square – I've never used a point of sale that allows you to write up a receipt for charity.
