How to hard reset disabled iPhone 8 plus when the home button is not working?

You don't need the HOME button on an iPhone 8 to reset it; it isn't a physical button. See these instructions-->If your iPhone, iPad, or iPod touch won't turn on or is frozen – Apple Support

I know with the phones that have a Home button that moved physically, doing a reset or restore wasn't possible if the button didn't work. I haven't tried on anything newer than a 5s so I may be mistaken about the process.

~Lyssa

Lyssa wrote:

I know with the phones that have a Home button that moved physically, doing a reset or restore wasn't possible if the button didn't work. I haven't tried on anything newer than a 5s so I may be mistaken about the process.

~Lyssa

It was a different device, but I remember my trashed iPad Mini 2. It was dropped so hard that the entire display had broken off and the home button was semi-attached but not working. It was still working, and would automatically connect to previous Wi-Fi. I could see it in Find My iPhone, and I could request a backup to iTunes since I had already connected before and it didn't require "Trust this computer?" I was able to do this for a while, but it no longer recognized it after I approved and it did an iOS update. Not sure what would have happened had I requested a restore to factory settings. That might require at least the Assistive Touch home button.

Does the home button not work at all?

If so, you cannot reset or restore it. It must be repaired.

~Lyssa

It might be possible with Assistive Touch, but it has to get out of power on to set it up at some point.