The 240-byte data starting with "U" can be an AES-256 encoded string containing your key.
You can easily decrypt it with the
openssl command if you remember your password or have some idea of what the correct password might be.
Here is the approximate command which may decode your key:
openssl enc -d -aes-256-... ... -in bitcoin-wallet-keys.key -out bitcoin-wallet-keys.dec
This command with several additional command line switches can decode your key, so you will be able to import the decoded key it into any bitcoin wallet app.
I recently managed to decrypt my 240 byte key file created in 2013 after the Bitcoin Wallet Android app failed to import the file because they changed the wallet file format.
Do not hesitate to contact me if you need any help with that.