Constant crash with plus signs on initial boot

I've tried both 10.14 and 10.15 installers, with similar results (just slightly different). Right after booting, it crashes. Without verbose, it just dies with the Apple logo on the screen. In Verbose, I get several messages (varies by version), then a string: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ (not the exact number).

I've tried FakeSMC as well as VirtualSMC, and I've tried minimal kexts as well as a wide variety of added kexts from Clover. I'm doing exactly the vanilla steps for the Mojave installer, and the MarkWithTech instructions for Catalina (not very different). I've rebuilt both installers from scratch at least once. I have disabled Vt-d and CSM, set to ACHI, XHCI enabled. I could not find settings in my BIOS for CFG-lock or for secure boot mode.

Any ideas appreciated. Here's my hardware, all brand new today:

Gigabyte Z390 AORUS PRO WiFi motherboard, F10 BIOS (latest)

Intel Core i7-9700K

Ballistix Sport LT 32GB Kit (16GBx2) DDR4

XFX Radeon RX 580 GTS XXX Edition 1386MHz OC+, 8GB GDDR5

Samsung SSD 860 EVO 1TB SSD

submitted by /u/calvarez
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