(1)
(a) "didn't see just Temporary Files category"
Oops, that's right, in 1809, at "START, Settings, System, Storage", you have to click the
(C:) drive to open the categories list. Then click Temporary Files to see the various items. In 1909, the categories are on the same page...

In the items list, careful you don't delete your Downloads. Those are better examined individually at "right-click File Explorer, Downloads" (good that you make backups). I just took in a new quality update (OS Build) & got a big
Windows Update Cleanup to do. I usually like to delete it just before making Windows system image backup...

(b) "I went to Storage and then into Free up space now"
In 1909, you get "Configure Storage Sense or run it now". I have it set to never delete my Downloads...

(2) OK. You sound good with AVG & MalwareBytes. I forgot to mention the AVG remover app. It's possible that $AV_AVGfolder will exist even when AVG is used just On-Demand. I guess it would be OK then.
(3) "Which 3 red X's?"
I meant the 3 showing under "critical events" in the bottom pane of your picture of 5/11/2020.
(4) I think the main thing is to get 1809 fully updated before trying 1909 again. We have to solve the problem of those NET framework failures.
(a) See whether the 1909 feature update shows up in WUShowHide now -- & block it.
(b) Then, I'd want these one at a time...

I hope we won't have to resort to the Microsoft Update Catalog.
(c) What is the OS Build that shows at "START, Settings, System, About"...?...

The latest one for 1809 is 17763.1217 -- but it just came out today. Before that, it was ...1192.