Read this
Put this instead.
<Installation InstalledByMsi="false">
<InstallationTarget Version="[12.0,17.0)" Id="Microsoft.VisualStudio.VSWinDesktopExpress" />
<InstallationTarget Version="[12.0,17.0)" Id="Microsoft.VisualStudio.Pro" />
<InstallationTarget Version="[12.0,17.0)" Id="Microsoft.VisualStudio.Premium" />
<InstallationTarget Version="[12.0,17.0)" Id="Microsoft.VisualStudio.Ultimate" />
<InstallationTarget Version="[14.0,17.0)" Id="Microsoft.VisualStudio.Community" />
<InstallationTarget Version="[14.0,17.0)" Id="Microsoft.VisualStudio.Enterprise" />
</Installation>
Version 17 is for VS19 (Helpful I know)
I have no solution yet, but you can use Windows Form Project then reference XNA dll.
If you only use Texture2D or SoundEffect, you can use FromStream Method (I tried this).
Or you can use other techniquess to create .xnb, either google it or maybe use MonoGame Content Builder to create .xnb (I didn't try this).
Maybe it's possible to decompile vsix and force it to create .xnb using some googled techniques, but I didn't try it.