Sometimes Apple insists on the old OS to be completely up to date before it will allow the system to be upgraded to a new major version of macOS. macOS 11.2.3 is a very old version where the latest is 11.7.10 (or there may be one slightly newer since Apple did just release an update the other day for some no longer supported versions of macOS).
If you selected a different volume for the installation, then it may have installed itself next to your current OS. In that case you may need to check the Startup Options screen to see if there is a second bootable OS on the laptop....if so, then it probably needs to finish Phase 2 of the install process.
You can try checking to see what Startup Disk options are available in the System Settings/Preferences. If you see two options for boot volumes, then you installed macOS to another volume alongside your current OS, but I'm not sure if a partially installed OS will appear on this screen which is why checking the Startup Options screen is best.