Is it safe to use an address twice (privacy excluded)?
I have read that if the random nonce k used for the ECDSA signature is not chosen at random then someone can calculate the private key.
Is this really a problem in practice?
I make a test transaction for new addresses to make sure that they work correctly.
I use Bitcoin Core 27.1.
You can reuse the addresses as many times as you want. In practice no one is going to be able to derive your private key just because you are reusing the public key that belongs to it. People say to not reuse private addresses for privacy, since they can see how you keep adding funds to the same address. You could always mix the address after you have a considerable amount and want to hide it from public eye.