EDIT - Not quite the fix I was looking for, it seems that DX11 uses this PCI-to-PCI Bridge to enable "feature level 10.0". On the bright side this is definitely a lead. Some games require DX11 feature level 10 too, meaning this doesn't really solve my problem, though it may solve someone elses.
Hello All
Leaving a message behind for those that haven't found a way to fix it yet. After going through a lot of suggestions and taking inspiration from Druid's posts I decided to disable devices in Device Manager one by one until I found the problem. One of the ten PCI-to-PCI Bridge devices under System Devices, right down at the bottom of the list.
Note that this will make Wallpaper Engine turn off and become unusable - DO NOT use Wallpaper Engine to set your wallpaper again it will crash your computer, infact I recommend you unistall Wallpaper Engine until Microsoft stop forcing broken updates or fix the problems they cause. It sucks but it's what we have to live with.
When I disable the offending PCI-to-PCI Bridge it makes my screen go black for a second and then return without the stutter that's been driving me insane all week. Enabling it returns the stutter even with Wallpaper Engine uninstalled, I'm certain it was the update rather than Wallpaper Engine.
If this doesn't fix your problem I recommend you disable devices one at a time until you find the offender, be warned though, some devices being disabled will not go well for you or your computer so make sure you know what you're disabling with a google search at the very least.
This is what a PCI-to-PCI Bridge is by the way - link to tomshardware.com
Incase it helps someone figure out what is wrong with the update I'll post the important bits of my system and list the problems I've had and the actions I've taken over the last week. Might not be helpful but you never know, I'll try to check back every so often if someone has a question.
System
CPU - AMD Ryzen 5 1600X Six-Core Processor
Board - TUF B450-Plus Gaming
GPU - NVIDIA GeForce GTX 1660
OS - Windows 10 Pro
Version - 21H1
Problems and Actions
>Began with video stuttering about a week ago, I reasonably assumed it was a Bethesda problem as I was playing 76 at the time and closed the game to start it back up. When I got to my desktop and the video stutter dissapeared but the mouse stutter remained I realised this was a Windows/my PC issue. I assumed it was the mouse and plug in a wired backup mouse, problem does not dissapear. No video or audio stuttering outside of playing games.
>Crashing frequently (no BSOD, as if it's plug was pulled)
>look up problem and try a ton of solutions including the ones in this thread
>Crashing stops mysteriously a few hours later
>Spend days researching and trying to fix the problem
>Still have cursor stutter two days later
>Complete PC reset, saved no files (This was a stupid move as now I have no idea which update it was that casued the problem in the first place)
>Still stuttering ... even while doing the widows setup (I gave up for a bit here)
>Cleaned inside my PC, made sure everything is plugged in properly
>Magically ran fine for two days after the clean, assumed that everything I knew about dust in computers was bogus and it really could cause damage other than insulating until overheating occured. (Installed Steam, Discord, that sort of thing)
>Started stuttering again, tones of research and trying to fix it again
>Discovered that Star Wars Battlefront 2 (2005) runs flawlessly (even in the menus and decided to try some other games at this point to gather as much information as possible for when I gave up and asked for help)
>Today I found all the first person games I installed (Fallout 4 & 76, The Outer Worlds, Skyrim SE, Call to Arms(an RTS that you can go into FPS mode, mouse stutters when not directly controlling a character in FPS mode)) run beautifully besides in the menus which the cursor stutters in (unless you play for 5+ hours in which case they begin to stutter video and audio which remains when you shut the games down and dont go away until you double restart the computer and leave it alone for 2+ hours)
>Looked for solutions for the final time and took the actions above and here I am
Thanks for the help and ideas guys,
Gogococo