Update: I contacted the builders of the PC and they advised me to enter BIOS and Load Optimized Defaults, then reseat M.2 SSD. Still the same after that so it looks like the drive failed. Might be able to get it replaced under warranty.
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The important stuff is backed up to one drive and Google drive and I'm hoping the failure of the SSD won't affect the files I've stored on the HDD. I can redo those though, if I lose them.
Awh yizz, awesome. Sounds like a setup for a reasonable IT-person. Fingers crossed although SSD failures tend to be fatal in pretty much every occasion.