Can't use dropbear private key file

[pwFoo]

Tried to use the branch with key auth, but doesn't work with dropbear generated rsa key.
Key seems to be valid with dropbear, but is unparseable for reverse-ssh?

dropbearkey -f /root/.ssh/id_dropbear -y
Public key portion is:
ssh-rsa <KEY> root@<HOST>
Fingerprint: SHA256:<FPRINT>

The ID file isn't a readable file?

Tested with a ssh-keygen generated pair and that seems to work.

But looks like binary uses the password instead of the rsa key...?

2023/04/04 20:53:42 Successful authentication with password from reverse@83.135.165.119:17424
2023/04/04 20:53:42 Attempt to bind at 127.0.0.1:8888 granted

Key file is read without an error. Debug lines say auth by password?
Is there a option to disable password and only use key auth?