MBP retina 13" e2015: with 10.15.3 unable to open files, launch certain apps

Short version: after update to 10.15.3,

• Some apps don't run
• Finder claims many files are "damaged and can't be opened. You should move it to the Trash" when the files are actually fine and can be opened from within the relevant app
• This includes installer DMG
• Disk Utility in recovery mode runs and finds nothing wrong

Long version:

Hi all,

I updated Mac OS to 10.15.3 from 10.15.2 last evening, and now I can't launch Chrome, MS Word, or MS Excel. Finder thinks thinks they're running in Force Quit Applications, but they bounce a long time and never spawn visible windows. I tried downloading Chrome to reinstall, but I can't open the DMG. When I try, Finder tells me the file is "damaged and can't be opened. You should move it to the Trash."

Meanwhile, I can run MS Powerpoint and Preview, along with many other apps, and I can open files from within the apps — files that Finder otherwise claims are damaged.

I rebooted into Recovery Mode and ran Disk Utility's repair on the root and "data" partitions of the hard drive, which seemed to work but flag nothing wrong. Same problems persist after normal reboot.

Back on Jan 1, I updated from an earlier version (El Capitan maybe) to what must have been 10.15.2, and this machine had a similar problem at first, with Finder unable to open files and complaining about "damaged and can't be opened." I believe what I did then was a full disk erase and reinstall, because reinstalling Mac OS did not solve the problem.

A similar thread appears to be here: https://discussions.apple.com/thread/250893357

No solution per se but a suggestion to erase and restore.

Thoughts? Thanks.

Hardware: MacBook Pro 13" retina, Early 2015