same issue, mac mini 2018; even with wiped and freshly installed system with nothing except HDMI and ethernet plugged in, no additional SW added, merely logging in and letting it sit would reliably crash it after 25-26 minutes. Took it to "genius" bar last week, they kept the machine for a few days and said they couldn't repro. I brought it home same setup and it was fine for a whole day -- they didn't admit to having done anything to fix it but I was happy. That wasn't long-lived. Now it has crashed every day or two which is less frequently than before but problem persists. Also note this happened last summer too and the geniuses recommended I replace the logic board last fall (cost me almost $500), which also did not fix the problem -- a problem they refuse to admit there is ("our diagnostics give it a clean bill of health") Shame, Apple