... can be very clever sometimes.

... already installed the security update, per another thread that warned about it.

More threads about it can't be bad, to help inform more people.

Try again later.

Not feeling good.

Sometimes the battery needs to be above some minimum threshold of charge, or it needs to be plugged into a charger, before updates can be installed.

Just throwing that out there, hoping it's a solution for you.

I later looked up that message online, and here's a list of possible explanations:
https://osxdaily.com/2021/03/24/fix-unable-to-install-update-ios-ipados-error/

Since their servers are surely getting swamped with today's update, maybe trying again later will really be your solution?

Next up: remove messenger from the iMac. I never use it anyhow.

so there's no patch that I can install.

It's a good thing that I'm not a politician or a high-level journalist, as the hackers will probably leave me alone.

Tried the Big Sur update on my iMac this morning and kept getting a notice saying there was an error with the download. This is a common problem for me whenever I try to update. Will have to work on it this evening.

iPhone, watch and iPad are up-to-date now.

It took me a while yesterday, and I had to hit retry I think on the iPhone. Jammed servers. I needed more patience than usual.