In my experience, only one thing can break a motherboard: The PSU (Power supply). In this case, we can think that not only the motherboard is broken but also CPU, Memory, GPU and also SSD (especially NVMe), in rare case SATA Drive also.
In any case before thinking about a broken mobo's, you and/or technicien have already changed the PSU before the mobo's.
If I've understand, his setup isn't very old... 2 years around, maybe 3... In case if he have no skill to repair his PC, it's also possible that he came across a technician who just wants to sell him a new PC instead of repairing the old one. I think also about "the massive eyeroll" too, but why don't tell directly that it's him that need a break instead of "broken mobo's" :x
Also, working type, how you manage your PC doesn't really affect his life, on my side, I use the same PC for gaming and working (dev, QA, testing and some loca) I never got an issue, except one because the PSU power was very limit after adding a HDD.
Short HS:
If you are interested, I can maybe think about translating the english part already done (not the MTL) in french.