Please note that this may not work for everyone, this just worked for me. Always back up your registry before editing it in any way. This only works for Windows.

0.5) Try running wsreset.exe first, it resets the Microsoft store.

1) Open Regedit on your PC
2) Navigate to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\Protect\Providers\df9d8cd0-1501-11d1-8c7a-00c04fc297eb
3) Add a new "DWORD (32bit) Value"
4) Name it "ProtectionPolicy"
5) Set value to 1
6) Run game, hope for the best.

So, how did we get here?

I'm including how I came about this just in case someone else wants to follow along.
I had the infinite sign-in bug which apparently is the game failing to load up the EULA on a first sign in. Every solution I've seen was to link/unlink/relink your Bethesda.net and steam accounts. Tried it, didn't work. Saw some people say they had success getting a friend's computer or a backup PC, loading it there and seeing if the game would work just so they could accept the EULA. Idk about you, I don't have a spare PC with enough space or minimum spec to even open F76, and I'm not about to sign into my steam on someone else's computer (or make them download a 100GB game) just to click "I agree".

I learned that the game was on Xbox's Gamepass which I only have from a friend giving me a spare 3 month code. Decided to try it through there and got hit with Microsoft error 0x80190001. Fixable by running wsreset.exe. Started up the Gamepass version of F76 and got a new error, 0x801901f4. Research led me to find that it has something to do with Microsoft Office failing to sign in or something, feel free to look it up on your own. I did find the registry edit steps listed above and I ran F76. Got past the EULA and into the sign in screen. Since I'm not paying a monthly Gamepass subscription and my free trial is about to run out, decided to try the steam version. My steam and Bethesda accounts were already linked, so I was immediately put into the game main menu and was able to start the opening cutscene.

I'm not a computer expert by any means, so I can't help you if this doesn't work. The only reason I tried the Xbox version was because maybe the Microsoft sign in wouldn't have the issue, and instead lead to an entirely different issue that apparently affected both versions. But, in a sea of everyone repeating the same two solutions and everyone else saying that it did/didn't work for them, I figured I'd offer up what worked for me. Worth a shot to someone who might be in the same boat, but doesn't have the crazy internet and specs that I do to test such a wild theory.

For the interested, here's my specs. Maybe they have some bearing on why this worked for me. (Motherboard is hot because my fans suck, don't worry I'm replacing them.)