Does the "Security Update 2020-001 Catalina" install BigSur and replace Catalina 10.15.7?

Thank you etresoft.

I have the settings as shown though it does say a restart is required. Part of what made me ask.

When I upgraded to Catalina, it was accidental. I had intended to upgrade to HighSierra from El Capitan. Those changes were much more than I'd bargained for at a very busy time of year and suddenly needed new everything. Still can't find a replacement for my minify app at the app store so I'm transferring files back to my laptop (HighSierra) to optimize css files for upload - but that's a different problem. Your answer will let me upgrade what I have so I appreciate your taking the time to respond. It lets me feel safer. Thank you!

Thank you again! I have been searching at the app store and only two such apps showed up, both with unwanted features and poor ratings. Maybe because I was searching for a css compression tool rather than a minify tool. This does look better and a lot easier than swapping files back and forth to the laptop. It looks similar to the old one I used for years. I will revisit the app store.

BTW, the security update installed smoothly (though slowly) and it seems to have fixed a number of issues I had seen since that accidental update. I prefer turning off my machine and then starting it (which does not work) to using 'restart' but I gave in and did it their way and it went fine. When it says "restart to install' that's exactly what you need to do.

I know I'll need to go to BigSur one day, just don't want to be in the first wave. The latest updates add on a lot of 'cool features' which I have no use for - and less when they break my tools.

Thank you again etresoft, I do appreciate your help here!

I installed that Minify app, used it on two files and then removed it. It doesn't minify the files so much as gzip them. I don't need an app for that. It has not been updated for years and when I used it, it popped up a window to a different site that showed a different owner and was not a secure site. It left a lot of manual editing to actually minify the file to remove unnecessary whitespace. For example the ending semicolons remained as in '16px; } ' which should have been '16px}' and it left a space after the closing bracket } and the ':' for each element.

I decided to just write my own apple script...when I have free time. I still appreciate the suggestion, it might have been just what I was looking for. Just thought anyone who might stumble onto this should know what it is.