Due to environmental concern, I would suggest to accept donations in cryptocurrencies only if they are not based on PoW. As of today, eco-friendly alternatives exist: major blockchains, such Ethereum, are now based on Proof-of-stake and do not waste huge amounts of CPU/GPU/ASIC cycles and energy in trying to guess numbers…
Iiuc number crunching still happens, but with much less redundancy and waste.
Should they refuse donations from fossil fuel industry workers? From travel or vacation industry workers? From internet industry workers? From…anyone who profits using energy?
Nice plug for ETH though.
I think for now, the project being small as it is, all donations are welcome to make it grow. Not only that, but as justsomeguy mentioned above, other methods of donation also require energy which may lead to waste.
For now, F-Droid should be open to as many ways of donating as it can. IMHO.