I just switched PCs from another Win10 machine, but I'm having a new issue:
Whenever I have DisplayFusion Multi-Monitor taskbars turned on, no matter what my other settings are, all the text on Buttons on my second monitor taskbar is black and impossible to read against the taskbar. The clock is white, but all the app text is black.

For example, "Untitled - Notepad" is basically invisible until I mouse over it to turn the button slightly grey.

My primary monitor doesn't have the issue, nor does my secondary when I use Win10's taskbar instead. They have white text on the black taskbar.

I searched around, but this doesn't seem to be a known issue?

Apparently themes were indeed the problem. I reverted to a Windows Default, then put all my changes back manually, and it fixed it.

I believe the cause was a simple theme I downloaded that was attempting to change the background area of app windows. I'm not sure why it affected DisplayFusion's text color though, since it didn't try to modify text color:

----------

[Theme]
DisplayName=Beige

[Control Panel\Colors]
Window=228 228 228

[Control Panel\Desktop]
TileWallpaper=0
WallpaperStyle=10

[VisualStyles]
Path=%SystemRoot%\resources\themes\Aero\AeroLite.msstyles
ColorStyle=NormalColor
Size=NormalSize

[MasterThemeSelector]
MTSM=DABJDKT