No real horror here, just blunt pain.
My mother has a laptop that wasn't cheap enough to justify just throwing it out of a window, but wasn't expensive enough to be actually usable when running W10.
She actually bought it with W10 pre-installed, but as it turned out a couple months later, it was originally a W7 machine with W10 updated on top of it. Off to a wonderful start here.
She had me back up "everything important" ("-What exactly, ma? -WELL I DON'T KNOW SON, EVERYTHING THAT LOOKS IMPORTANT!") then took it to a repair shop to wipe the drive clean and install everything fresh.
Now, with a clean W10 installed, it's still fucking slow and barely usable. Why? Because she doesn't use it frequently enough so the system needs to do everything exactly when I'm trying to fix something/help her with anything minor that doesn't need to be taken to a shop. Look for, download, and install updates, MS Defender, Windows Removal Tool, everything.
And she never shuts it down, just puts it to sleep "so it boots fast". I've offered to buy her an SSD but "-No, the repair shop guy said the laptop is a pain in the ass to disassemble and reassemble and I'd feel sorry for him if he had to."