Using a key specifically generated with ssh-keygen -t rsa-sha2-512 on a Ubuntu 18.04 server running OpenSSH 7.6 (possibly others) erroneously reports

You're using an RSA key with SHA-1.
This key will continue to work if it's already set up, but you should strongly
consider generating a new key with the following command and using it instead:
ssh-keygen -t ed25519
If the key hasn't been set up by the deadline, you'll either need to generate a
new one as listed above, or upgrade to OpenSSH 7.2 or newer.

The debug statement for this version of OpenSSH for the sign_and_send_pubkey looks like debug3: sign_and_send_pubkey: RSA SHA256:<KEY_IDENTIFIER>. It is missing the 'signing' portion that the script is expecting. However, adding this key to a repository and cloning still works since the key is valid.

I just added a ssh key to my profile as instructed in https://docs.github.com/en/authentication/connecting-to-github-with-ssh
authentication with ssh -T [email protected] is successful
then I run the script:
jano@cata  ~  /usr/bin/sh ./ssh-key-algo [email protected]
using: /usr/bin/ssh
You're using an Ed25519 key. You're all set!

then I try to clone something:

jano@cata  ~  git clone git://github.com/DreamSourceLab/DSView.git
Cloning into 'DSView'...
fatal: remote error:
The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.

I cannot clone, is the script lying or am I doing something wrong?

I have two systems each running Xcode Server. Since around the 16th, both are unable to sense commits to repos and therefore do not trigger builds. When I investigate the server bot settings, I see the message that "SSH fingerprint could not be verified". I told both systems to trust the fingerprint, and all was good for one week. Then it happened again yesterday, and a colleague pointed me to the github blog post: https://github.blog/2021-09-01-improving-git-protocol-security-github/

I rotated one system to ecdsa, and this morning I realized this ssh-key-algo script exists.
So I ran ssh-key-algo on the server that is yet to update and I'm told "You're using an RSA key with SHA-2 (algorithm rsa-sha2-512). You're all set!"
That is the same key type that was failing on both of my servers. The ecdsa system also tells me "You're all set!" but this morning I see that server encountered a fingerprint problem again after updating in accordance with the blog post.

I can't tell if this means that this script is giving me a false positive, or if there is something deeper wrong.

When I do this:

./ssh-key-algo.sh

I get

using: /usr/bin/ssh
Could not authenticate to [email protected], and could not understand your key type because of that.

What does this mean?