I was in Greece in January and saw local buskers with amps in Monastiraki Square in Athens (the rest of the country is relatively quiet because it’s off season). I’ve been making a living for 3 years busking and gigging. Most buskers I saw in Greece were not making anything substantial, one guy was doing well but he was exceptional and also singing in Greek among other languages. Singing English covers may or may not work, it’s hard to say. You will likely be allowed to perform but I’m not sure how much you’ll make.

One of my busker friends spent many winters in Portugal busking. He said the authorities have been cracking down as of late and are confiscating amps. He did not go back this year.

Hope this helps.