I had a same problem. Just formatted my PC, and I followed some tutorial step to install VS code and the tutorial includes installing the VS buildtools which is apparently get installed once more if you install vs2019 afterward,
to fix it, I launched the VS installer, then proceed to uninstall everything on the installed tab, restart the computer, then reinstall the VS2019 checking only the required workload (for gaming). UE4 now launch VS2019 properly.
For your case, perhaps try launching VSinstaller and see if there’s overlapping buildtools installed, for me the telltale was VS2019 was installed with a suffix"(2)".