Obviously it's a busy day. I don't use any of the built-in Magix VST's, so disabling them is fine for me, but it would be odd if I'm the only one who sees that dialogue box. Clean install on clean install of Windows 11.
This VST problem on opening Vegas Pro 20 has been happening on-and-off for ages - and it happens with Sound Forge Pro 16 as well. I've done the added coding in the anti-virus program but alas to no effect. Sometimes it's a VST2 problem, other times a VST3 problem.
Remove the problem plug-in's <.dll> file (if uninstalling the plug is not an option) since it will not work anyway. The VST-2 plug-ins are often in the "Steinberg" or "VST" folders in 'Program files'. The same folders if they are 32 bit VST-2 plugs.. except they are in the 'Program files (x86)" folder. VST-3 plug are in 'Program files> Common files> VST3'