1. I had a windows 7 installation with 5 versions of Corel's video studio installed - licence allows that, but only running one version at a time.
2. Video studio uses Visual C++ redistributables, several of them per version, and some are common to different versions. Windows 7 runs multiple program installations without a problem, but win10 will only allow one.
3. Upgrading to win10 - 2 attempts using the recommended in-place migration method - yielded a good win10 installation, but when video studio was installed, the second version installed "captured" a re-distributable used by the 1st version, leaving it "broken". See 5 below for how
4. Because VC++ redist for win7 and win10 are incompatible, they were uninstalled before the application was installed under a migrated win10 platform. On the 1st attempt the re-dist were uninstalled after migration, and on the 2nd attept they were uninstalled before the migration. The application installer determines and downloads the redist wanted to suit the (in this case, win10) OS on the PC.
5. when VS X10 was installed as the only VS version on win10, it started Ok and selecting a share page to render a video opened correctly. This page uses VC++ redist to display. The P&F page of control panel showed 4 redist versions when only X10 was installed.
6. When a second VS version - 2020 - was installed, it also started Ok. The share page opened correctly when selected. However, closing 2020 and starting X10, a share page selection now fails: hung up. Task manage close program is the only way to escape this.
7. When the 2 versions of VS (x10 and 2020) are installed, P&F shows 6 redist versions. Two are clearly extra for the newer version, however the other 4 are also used by 2 versions. And the later version seems to have reserved 1 (maybe more) of them for it's own use. This should not happen.

I've been unsuccessfully asking why or how this could happen on a new win10 platform - twice. It cannot be a coincidence, and it seems like it's a setting made somewhere. So far, there haven't been any answers. This is another attempt to find out why . . . .