Answer by urpok23 for Convert a hex string to base64

Since .NET5 it can be done using standard library only:

string HexStringToBase64String(string hexString){    // hex-string is converted to byte-array    byte[] stringBytes = System.Convert.FromHexString(hexString);    // byte-array is converted base64-string    string res = System.Convert.ToBase64String(stringBytes);    return res;}

Also there are good examples in docs