Have Inspiron 5567 that's slow to boot with black screen, backlight is on. TM states disk use is 100% when it does boot for 1-2 minutes but can't pinpoint cause. Win10 reset done with keep files option. Has Toshiba 1TB drive, healthy says sfc, chkdsk & DISM utilities, BIOS v 1.2.3. "If you shutdown now, you and other people will lose information" seen when shut down from lower right corner of pre-login screen image, although I'm only user and have tried signing out/in, no difference. No malware on machina. Windows Defender & Malwarebytes A/V.
After Windows loads, does the computer seem to work faster? If so, I would look into upgrading the hard drive to a SSD, or if your computer supports it, a M.2 NVMe SSD. I also have a 1TB Toshiba hard drive in my Inspiron, and Windows does take a few minutes to load, much longer than my last laptop. (Must be a low end entry level drive). I too, I'm looking into upgrading to a SSD.