Apple makes it hard. Before Big Sur, one could download macOS point updates as Delta or Combo updaters for use with more than one Mac. It’s even harder under Big Sur because point updates are not applied to clones even though the main boot-up drive from which the clones are made do get updated. Since I have or am responsible for three Big Sur Macs & four clones thereof, I need something relatively simple.
Therefore today I downloaded the macOS 11.2.3 installer & used Disk Drill (via Setapp) to create a bootable installer on a spare 250 GB external USB-C SSD. Right now it’s updating the iMac’s clone to make it into a bootable 11.2.3 system.