This is what immunologists are saying pretty much everywhere you look. I thought "AFAICT" was clear enough that 1) I have tried to find this out and 2) from what I can tell the preponderance of opinion from people who seem qualified to say so is that your immune system doesn't "weaken" because you are avoiding infection. Even TFA quotes an immunologist calling the idea of individual-level immune system weakening "nonsense". I could also be wrong or looking at the wrong sources. I don't want to stop anyone from looking this up themselves, finding out what experts are saying, and making a judgment of their own. We don't have to stick with folk science or what "sounds plausible".
My comment was mainly to point up the analogy for seeing more infections today primarily because there were fewer infections before, not primarily because everyone's immune system is weakened. There are of course other concerns with disease burden and herd immunity overshoot. I do fear people are stretching the Windows Update analogy too thin, as your immune system isn't a computer and the dynamics are more complex (e.g. it doesn't matter if you avoid Covid Alpha and don't ever become perfectly immune to it, because there is hardly any of it circulating anymore, and your Omicron infection has some cross-immunity).
My comment was mainly to point up the analogy for seeing more infections today primarily because there were fewer infections before, not primarily because everyone's immune system is weakened. There are of course other concerns with disease burden and herd immunity overshoot. I do fear people are stretching the Windows Update analogy too thin, as your immune system isn't a computer and the dynamics are more complex (e.g. it doesn't matter if you avoid Covid Alpha and don't ever become perfectly immune to it, because there is hardly any of it circulating anymore, and your Omicron infection has some cross-immunity).