That Vegas Pro is stalling when scanning for VST plugins suggests that there might be a VST (audio) plugin that is not compatible with Vegas Pro. Do you have any audio plugins - VST2 or VST3 - from 3rd party companies? If yes, which ones? And it be worthwhile if you check those plugin product websites to check for host compatibility.

Very probably, Vegas Pro is scanning for VST plugins in:

C:\Program Files\Steinberg\VstPlugins; or

C:\Program Files (x86)\Steinberg\VstPlugins; or

C:\Program Files (x86)\VstPlugins (this folder may or may not exist)

One possible way to identify a problem VST plugin is to remove all the .dll files from those folders (storing them elsewhere) and then it would be expected that Vegas Pro should open; then close Vegas Pro, copy back to the relevant VST folder a few of the .dll files at a time and see if Vegas Pro opens. If it stalls on opening again, you're in a better position to drill down to the problem VST plugin/s.