Hi Johannes,
If you use C or C++ TO develop on the computer, Error: stack-buffer-overflow is not a problem, check the following document to deal with it.
Error: stack-buffer-overflow
https://learn.microsoft.com/en-us/cpp/sanitizers/error-stack-buffer-overflow?view=msvc-160
Since antivirus scan hasn't found any malicious software, I think your device is safe.
About installed-updates view, you could check the Windows Update history website, compare the latest build with your current build, in general, we don’t need to care about every update, because later update will include all content of previous updates, install the latest SSU and CU is enough.
For 20H2 version, March 18, 2021—KB5001649 is the latest.
https://support.microsoft.com/en-us/topic/march-18-2021-kb5001649-os-builds-19041-870-and-19042-870-out-of-band-ebbe0617-3a63-467a-aaaa-2a4c68a6de33
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