I have mentioned that also against the development team. But here I cannot promiss anything, sorry to say so.
Maybe another possibility: do you have an image of your system drive, that you could try to playback? Because something must be wrong here with your specific machine - since the b403 seems to work elsewhere (for me at works like a charm).
Worse case scenario advice/solution: A few years ago I found myself in the exact same situation, where VEGAS Pro just refused to open. Some other program or bad Driver, caused damage in Windows, that badly affected VEGAS Pro. I wasted 3 days of my life and nothing worked. The solution that DID finally work, was to reinstall Windows. Yes it is a pain to reinstall Windows, but it solved the problem and only took a few hours to complete. Reinstalling Windows is sometimes the best thing to do and will save time and frustration in the long run. If you did this, you can get VEGAS Pro 20 working quickly, finish your important project, then reinstall all your other programs after the important work is complete.
Two weeks ago, Vegas Pro 20 was behaving very weirdly as were other things Windows related on my desktop. I seriously thought that a repair/re-install of W11 was going to be needed. But a bit of researching on the web found the suggestion that andyrpsmith has suggested just above, but preceded by running a DISM check as per:
Dr Zen : why not reinstall windows 11 but it's a fresh install from less than 10 days ! I can't beleive something happened ^^ IF no solution within 1-2 days i'll try this solution but with not a lot of hope ^^