Cannot save games in FE:LH and SK:R, Save/Load window is always blank

I have 2 PCs.
FE:LH on the old PC saves games fine (and the new one sees them).
FE:LH on my new PC cannot save at all.

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A. FE:LH on old PC works fine
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+ IBM Thinkpad, Windows 7 (never upgraded), does not have Microsoft OneDrive.

[x] FE:LH saves to Steam Cloud OK, sees default saves (Carr Stab.EleSav c. 2015), can Save normally, sees my own saves, can Load normally
[_] (I never installed Sorcerer King: Rivals on the old PC)

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B. FE:LH on new PC always shows blank Save/Load screen, saves nothing
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+ custom PC, clean install of Windows 10, no prior usage

[x] with saving to Steam Cloud enabled
[x] with Microsoft OneDrive installed

In FE:LH, all of the following are happening.
{
[_] Load or Save shows all-blank, does not see default saves
[_] clicking Save does not create any file on disk
[_] AutoSaves are not written to disk
[_] dynamic changes to Options, Basic or Advanced Options do not persist (exactly as if it can't write a config file to disk)

[x] when FE:LH on the old PC saves to Steam Cloud, FE:LH on the new PC sees those files
[x] when FE:LH on the old PC designs a unit and saves it, FE:LH on the new PC sees those unit design files
}

In Sorcerer King: Rivals (on the new PC), all of the above happen exactly the same way.
{
[_] Load and Save show all-blank
[_] Save doesn't create any file
[_] Autosaves don't save
[_] changes to Options don't persist
}

I've tried these work-arounds, with no success.
I've searched these Forums for "saved game", but found no prior answers.

 

[o] In Steam, right-clicking on FE:LH's Options and unchecking Steam Cloud results in the same behavior as above

[o] I've uninstalled and reinstalled FE:LH from Steam at least twice.  No change to any of the above.

[o] From Windows 10, I uninstalled Microsoft OneDrive (and rebooted several times since).  No change to the above behavior.

[o] My folder Users/$(me)/Documents/My Games/LegendaryHeroes/ is set to Read-Only, but individual files are not.

More generally, the entire C:/Users folder tree is marked Read-Only at the folder level.
"Changing" this setting doesn't change it.  It seems to be the normal state for a Windows 10 directory tree.
It doesn't affect any other app or game.