Speaking to Windows 10:
Young lady! I seem to be having the same issue as you. 🥶 VST (virtual studio technology) is quite the "industry standard" for a looooong time now.
The MixPad directory structure and location of the files infrastructure is obviously simple. From my search, it appears that MixPad stores its homegrown effects (*.efc) files at local [C:\ProgramData\NCH Software\MixPad\en\presets]. However these (.efc - not MS Outlook) files apparently are proprietary predators. 🤑 I like the MixPad Visual EQ for custom LP/HP EQ but it's a bit awkward setting my own "QFactor" band sweep manually - it's doable but with much patience and virtue. I really wanted to drop in the free VST plug-in MEqualizer | MeldaProduction but you know as well as I do it aint gonna happen with MixPad.
Switching gears, I also use another program that uses common (*.dll) files for VST plug-ins and I simply drop any "clean" DLL into it's native VST directory and the program will scan this directory and vwa-lah there she blows - literally.
So my dear, it looks like with MixPad we get what we paid for MixPad Masters v 7.30 "NO 3RD-PARTY VST PLUG-INS ALLOWED" ~$80. 🙂
Rock on Girl - Rock Guitar