Get a list of security patches installed in the last 90 days

How can I list all the security patches that I’ve installed in the last 90 days?

There’s a class for that! Just use Get-CimInstance, and you can retrieve this information. Here is an example:

Get-CimInstance -Class win32_quickfixengineering | Where-Object { $_.InstalledOn -gt (Get-Date).AddMonths(-3) }