iPhone 8 Plus broken rear glass: The glass on this back case shattered 2 weeks after purchase, when my daughter dropped the phone without a case on it. For 4 years it functioned with shattered glass taped up, and a case over it to hide the debris. When I inherited the phone from her, I knew I had to attempt this repair. There are YouTube videos showing how to "remove" the glass, and there are sellers who sell replacement backs for the phone.
I bought a heat gun from eBay to add to my arsenal of tools. I used a single-edge razor blade, lots of heat, and gloves to protect my fingers from cuts. THIS WAS THE HARDEST REPAIR I EVER DID! Chipping off the glass piece by piece, prying tiny edges and heating and reheating the chunks was horrific. I'm not sure if gripping the back of the razor blade or the 80 ºC temperature was more painful. I could not move my fingers for two days afterwards.
But the glass did come off piece by piece as promised, and I even preserved the wireless charging patch. The photo of the phone back with the glass removed shows my success. However, as a last step it is necessary to remove the little metal housing around the cameras. It was not clear from the YouTube videos that this is difficult to do. The cameras are pressed into this housing, so the housing removal yanked on them. Had I known, I could have prized them out of the housing from an exposed corner. Final result: two broken cameras.
Fortunately iFixit sells the camera pair for this phone and posts a beautiful repair guide. The replacement camera quality was fantastic! I also replaced a failing earpiece speaker. So after an additional $100 of parts, this $1000 phone was back to new condition. It is far larger than what I like (don't know why a college girl would want this) but I am proud of the repair.
Incidentally, I reinforced the adhesive that came with the new glass camera back by adding 5-minute epoxy. So I certainly hope that I won't need to attempt this repair on this phone again.
My advice is not to attempt this repair unless you are a true glutton for punishment. As shown in YouTube videos, it is true that it is possible to do this repair. But I would rate this only appropriate for a super experienced repair hobbyist, with strong fingers. On the bright side, it costs only pennies compared with the replacement from Apple for this damage.