MACBOOK PRO Software Updates

Since there's nothing stated in your Q: ~ to say what you did, or did not do;

the following article has links to additional options; maybe some forward:

"If your Mac isn't compatible, you might be able to install an old version of macOS instead."

Some build models were on fringe for upgrade, Or had contributing

factors w/ their configuration, that held them back from a full upgrade.

On the face of this question, there are several plausible replies; or answers.

Updates are fixes for the current major version.

If you want a different major version, you need to look at UPGRADEs, which are handled more like new purchases, but on sale for $0.

The article cited at the top regards UPGRADEs.