Are you sure you have an RSA key and that’s what you’re actually sending? From the server message, it clearly says it accepts RSA. Why don’t you just generate a new RSA key with ssh-keygen -t rsa and try that? On some systems, it defaults to Ed25519 so you need to explicitly set it to RSA.
What is the output of ssh -v when you connect?
Just in case you’re actually using Ed25519, you should know it won’t work if the OS is running in FIPS mode.