Looking at the error, `send_pubkey_test: no mutual signature algorithm` usually hints at a more recent OpenSSH client that no longer supports certain algorithms and hence you need to whitelist them.

You can issue:

 ssh -Q PubkeyAcceptedAlgorithms

To get a list of allowed algorithms.

I took the solution from atlassian [help][1]

Add PubkeyAcceptedKeyTypes +ssh-rsa to ssh_config

Another solution is

 ssh-keygen -t ed25519 -C "[email protected]"

To create a new key, add to `ssh/authorized_keys` and you should be good to go.

 [1]: https://confluence.atlassian.com/bitbucketserverkb/ssh-rsa-key-rejected-with-message-no-mutual-signature-algorithm-1026057701.html