When I go to Settings and then click on "Update & security" no window/dialog appears... and the "Settings" window/dialog also disappears.
I have also not been notified of any Windows updates needing installation for about 2 months.
I should perhaps mention that I loathe Windows more than death... and for that reason I went (after installing) to some lengths to ensure that no "updates" were ever installed automatically (disabling the Windows Update service, turning off use of it "because I'm on a metered connection", all that nonsense).
Instead, what used to happen was that at the end of every month I would check (via "Update & security") for any updates which I supposedly had to install... and then I would head off to https://catalog.update.microsoft.com to pick up and download the individual update programs (usually beginning "KB...").
Actually I can run Windows Defender separately (virus and spyware protection up-to-date), so I don't have any particular need to access this "Update & Security" dialog, although it would be good if I could get it back. Failing that, is there a way of determining from some website what downloads from catalog.update.microsoft.com I should be installing?
NB I am able to obtain a list of installed updates (View installed updates) present in my W10 OS.
NB googling around for solutions I seem to have found that there has been a particularly pernicious M$ "update" in April this year. Perhaps it's good I missed out on this.