If I donate XMR to e.g. the developers of a free software project, how are taxes handled? Is the developer assumed to report his profits to the state and handle the taxes or do most devs just keep 100% of the donation?
If it would somehow be made public that I donated x amount to a dev and that neither of us payed taxes, would the dev be taken accountable or me or both of us?
You should obey all your applicable tax laws. If you realize a taxable gain on your Monero holdings you should pay tax.
If you donate Monero to someone then they are responsible for the taxes on their end.
Obviously consult your CPA, Accountant, tax attorney for actionable advice.
That makes sense, thank you!