But that's not true! Earlier on you mentioned the starter was clicking which means that you're getting power to the dash and the starter circuits which is better than only one or none of them.
Real quick, here's the wiring diagram:
https://www.ft86club.com/files/BRZwiringi.pdf
If you're just getting clicks then there's clearly not enough juice going to the starter. I saw you were gonna check the starter from an earlier recommendation, that's the best place to start.
Next, Is there any wiring in there that looks off? I know you said stock, but if it's used it may have been returned to stock for sale. I'd start looking for some spare sub amp wires in the trunk, or splices on the harness. If someone did audio upgrades incorrectly, then left some things out of place after going back to stock it's not impossible that things shifted around. I'd also check on every fuse for both amperage and continuity.
Beyond that, it's possible something on the ignition circuit has gone awry, but again you've got clicks but not a turning engine. Best I can come up with for that is an immobilizer issue.
I guess maybe something could have frozen up in the block. If that's the problem we're waaaaay outside the ballpark, around the corner into the alley, and behind a dumpster for how unlikely it is.