strange notification on boot up

2 days ago I botted my iMac late 2015 with mojave 10.14.6.

The display opened with a small notification window at mid screen. About 3x4 inches, the window contained the words "APPLE WANTS TO MAKE SOME CHANGES."  THE ONLY OTHER THINGS IN THE WINDOW WERE THE "CANCEL AND THE  "OKAY" SELECTIONS. NO 0THER INFO GIVEN.

I was concerened and had to click the CANCEL buton 4 times. Finally the litlle window disappeared, leaving no ifno or trace that I can find. ANYBODY HAVE A SIMILAR EXPERIENCE?