I'm still having a hard time deciding what to do for my wife when her 2020 i7 5K iMac (maxed with 128GB RAM) finally dies. It's been a real workhorse but also randomly reboots once or twice a day when she's working it hard. I haven't been able to figure out a common cause, the crash logs tell a different story each time about what was in memory/what it was doing when it crashed, so it doesn't seem to be one particular program.
She's started using her 16" MBP M1 Pro more and more, so I think the eventual solution would be to get her a dock and a Studio Display or maybe the LG to save some money. Someone still needs to come out with a more affordable plain 5K monitor with no webcam, speakers, or other misc junk to drive up the price.
It’s possible that dust is causing issues. Those later-generation Intel iMacs ran really hot under load, and IMO the ventilation was never optimal for “heavy workload” type uses.
The original 1998 iMac was, in the parlance of that time, more or less a “thin client” type computer. I think Apple has gone back to that approach to the iMac, and Apple going back to the color schemes tells me as much.