So, today I did the unthinkable. I allowed Windows Update to look at my system. (I told SledgeHammer to temporarily allow updates.)
My system is Win10, 2009, aka 20H2. (Why all the numbers MS?)
The update page was confusing to me.
Initially, it said that it wanted to download KB4580419 and KB4586876,, which are cumulative updates for NETFramework.
So I let it download those two KB's.
But after rebooting, the KB listed in Control Panel (View Installed Updates), installed today (12/5/2020) neither of these KB's. Instead, it was KB4578968, an update from October 2020.
While I'm posting about this, here's what NTLite wants to offer me. It's the same two KB's for NETFramework as MS. (Although the dates of the MS KB's are later than the dates shown in NTLite.)
I don't see KB4578968 in the list.
Also, note that NTLite wants to offer me these two KB's even though I just downloaded them via MS's Updater and, presumably, installed them.
Yeah, I'm confused.
In any event, HandBrake opens fine now. So apparently the updated NETFramework is working okay on my system now.
(But I don't know why.)