What's the best BTC wallet that can run on desktop and fully open source? I'm mining through Nicehash website using GPU but getting paid in BTC and I want to store BTC as long as possible that's why I create this topic here, hope I'm in the right section.
You asked for a desktop wallet, but for
storing BTC as long as possible, I would instead recommend some sort of cold storage.
Either an
open-source hardware wallet or something DIY like an offline seed, created from a laptop running Tails live off of a USB stick. If this sounds complex, have a look into
SeedSigner - that's the same thing (tiny offline computer), but basically preconfigured and easy to use.
If you buy a hardware wallet, to keep your privacy make sure to
install Bitcoin Core and
electrum server on any computer that you control; then connect to this node
(by entering the electrs Tor URL) from any software that is compatible with the wallet of your choice. This software could even be a mobile app, if your hardware wallet supports mobile phones.