It's not hard to test out and figure out what's causing it. It shouldn't be Steam because that doesn't even run at startup. You can image (Reflect is great and free) your current C: drive so then you can fuck around with Windows installations and then just restore that image when you figure out the culprit. There's really no reason to even fresh install Windows when you can restore images, like I never did a Windows install on my new laptop or desktop last year, I just used the image off my older laptop and loaded it on the new desktop and laptop because I'm not re-doing all my Windows and program settings, registry edits, group policy edits again. I'm sure you'll find people saying doing that is a big no-no but it works flawlessly (just uninstall the drivers from the previous computer's mobo, CPU, etc and install the proper drivers).
Try doing a fresh install, then run the
debloat script and see if it still hangs after that as that script removes pretty much everything while keeping Windows still working (though the Microsoft Store won't work anymore). If that still doesn't work, maybe it's some weird hardware problem. Microsoft programs like OneDrive will max out the CPU and disk usage at the start. Below is a pic of my work laptop after a restart with "normal" stuff like OneDrive, Teams, VPN running on startup and look how it's pinging the CPU, SSD, and network 3 minutes in still. Notice how there's over 100 more processes running (with nothing opened by me yet) than my desktop with everything I could basically have open at once. Plus, you'll notice my desktop CPU (pic from the previous post) is basically doing nothing a minute in while my work laptop is at 100% over 3 minutes in. Windows 10 has a shit-ton of baked in stuff that doesn't need to be running.
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