My dad got a 2017 MacBook Pro over this past summer new at apple store. Not refurnished or used. It came with High Sierra 10.13.something. I forget the exact number. But it was definitely High Sierra. Anyhow it was part the the hard drive recall. So I took it for an appointment today. They said the hard drive was not bad and passed the test. So they erased everything and installed new firmware. They said they have too. No way to install firmware without erasing everything and doing a fresh install of the os. I had everything backed up to iCloud so I was ok. Except photos. Don't have enough space. But I had a 64gb pen drive in my bag so I copied the library to that. All is good now. Anyhow. When I came home desret background changed to black for evening time. Then I realized I was using Mojave. I did not have High Sierra anymore. I don't think there was any specific apps that required High Sierra so I am fine. But were they supposed to upgrade to Mojave? They said erase and reinstall so I agreed. But couldn't they have just reinstalled High Sierra? Or since Mojave they don't keep High Sierra on the servers anymore? And if I realize I do need it at some point then I can't go back unless I find my old copy of the installer? And if I can't then I am stuck with Mojave if I have to or he does nt like it? Or were there any specific app that only run on High Sierra and will not work on Mojave?