I use QuietRSS which sets its User-Agent to "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.120 Safari/537.36"

Source: https://github.com/QuiteRSS/quiterss/blob/271c55756dcf19ca163a603a54d12f165548a602/src/main/globals.cpp#L98