macos – How to stop Mac OS from checking for and asking to install updates?

I am trying to stop my MacOS from periodically checking for updates and displaying these notifications:

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I have unchecked seemingly all relevant checkboxes in App Store preferences:

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And in System Preferences / Software Update as well:

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Yet every time I open the latter it defiantly checks for updates:

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How do I get it obey my directions? I am aware that some updates are required to actually fix security issues (as opposed to enhance the telemetry / data collection / spying etc. for the benefit of Apple). Yet I expect the OS to do what it apparently supposed to: not to check for updates if the checkboxes are unchecked (otherwise why would those checkboxes exist in the first place?). I am happy to take the risk to live without updates where I choose to, and I do not need Apple to override my decision.

This is Big Sur 11.3.1 (20E241).