How to update macOS to latest release of current version?

Solution 1:

Download and install the Catalina 10.15.7 Combo Update from Apple.

Solution 2:

You should be able to install the update with the following:

softwareupdate --install "macOS Catalina 10.15.7 Update" --restart

Solution 3:

The command line version of the macOS software update — /usr/sbin/softwareupdate — has the capability to ignore specified updates. The --ignore command line option performs the functionality.

From the sofwareupdate man page:

--ignore identifier ...
    Manages the per-machine list of ignored updates.
    The identifier is the first part of the item name (before
    the dash and version number) that is shown by --list.

Using this, you could tell the software updater to ignore the Big Sur updates and install any other available updates.