At home I’ve the 2017 iMac i7 5K. It would not probably connect with the keyboard and mouse. First they put in a new Broadcom chip, but I was experiencing the same issues. Than they’ve put in a whole new motherboard. Together with hours of phone calls and taking more than 6 weeks to repair, it was my most frustrating experience yet with a € 3000,- machine. They didn’t even lend me a substitute Mac in the meantime or any other compensation. On top of that the magic keyboard II bend over time like a banana. It was a known issue and Apple quietly revised it (that’s why it took so long in the beginning to order a new magic keyboard II).
This was for the first I wasn’t happy with my newly bought iMac. It felt If I had bought a refurbished iMac after the repairs because they had to cut the screen open twice to get to the inner parts and remove the glue.
The first time it got returned the glass of the screen wasn’t placed correctly. They made that right the second repair. All in all not a premium experience.