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
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.