Hello wastelanders.

Since today morning Fallout 4 hands me a boot to the butt roughly 5 seconds after the main menu loads.

I have not changed anything beforehand and tried many things already including Verifying Game Cache, updating graphics driver, starting the game beefed up to ultra, low in borderless window and nearly everwhere in between, employed every .ini tweak I know of ...

DXDiag

I hope somebody can help me fix that problem. I want to go back to boston, the minutemen need my help at the castle -.-

Of your 8 GB system memory, your system's integrated graphics are poaching 4 GB!
Leaving maybe ~3 GB for the game. Way below spec.

Beth the devs specify 8 GB for the game and a 2 GB vidcard (minimum).
You could probably use your integrated graphics, though not recommended or supported, if your rig had 16 GB system memory...
But right now, as it sits, things for you are inadequate.

EDIT: as your game progresses and your save file grows bigger and bigger, your RAM squeeze has apparently 'come to a head' as the saying goes.
This would explain why it used to function, but functions no longer.
See if you can configure the integrated graphics (in BIOS) to use only 2 GB memory not 4GB, which should be adequate.
This would free up another 2 GB for your game...
But the long-term solution for anyone in your situation is 16 GB system memory.
(Hey it's less expensive than a $300 dollar vidcard, right?)

Sooo ... just so I understand correct.

Even after I reset every option of Fallout 4 to default and delete the savegames thus they should not affect the game at all they still are bloating the game? (Should have continued mentioning all the things I tried instead of ... I guess. Things I did NOT do include update rollback and windows/game reinstallation)

And you noticed the crash happens seconds after entering the main menu, not after hitting "continue" where the savegame should? not be loaded yet?

The save games are loaded and parsed early. What happens when you remove the saves folder? Make sure the cloud is disabled also or else the saves will be restored.

Are you using mods?

Of the 8GB you have the integrated GPU is reserving half a gig (dedicated memory) not 4 GB. The 4GB includes main memory which the game is likely eating into as well.

The GPU is way below minimum requirements.

Answer to mods: Yes but situation unchanged if removed.

Answer to cloud: Disabled as well as Steam Overlay.

Answer to saves: No impact if present or not.

I Clean restarted multiple times. I cleanly uninstalled and reinstalled the drivers. I cleaned up registry + temp files. I did a HDD scan to find out if that thing is on the edge of failing.

As I said I tried nearly everything to no avail. At least everything I could think of.

Maybe it's some bull like forgetting to press F 13 times through windows startup or some shenanigan. I am totally out of ideas.

There are no "ideas".
The game cannot be expected to play on your rig. You need either more memory or a vidcard...
(Is there an echo in here?)