2008 MBPro Crashes when reinstalling Yosemite
The last version of OS X that Apple released for a 2008 MacBook Pro is El Capitan (OS X 10.11.x). If this Mac was upgraded to Catalina, then this must have beed done using some sort of macOS patch. The original state for a 2008 MacBook Pro would be Leopard, but you seem to indicate you think this is Yosemite. There have been reports Yosemite failing to boot after installation do to expired certificates. You have give no indication where you acquired Yosemite. Perhaps your statement &quot;it's a ridiculous undertaking to make a Yosemite boot USB while running Big Sur&quot; means you used your Mac to create the bootable USB Yosemite installer. If true, this still does not indicate where the Yosemite files came from or the method used to create the installer.
Apple has a website How to get old versions of macOS. I assume these downloads have updated certificates. If you use your Mac running Big Sur to create the USB installer for El Capitan (or perhaps Yosemite) you will first have to install Big Sur in a virtual machine. I have tested this using a free version of VMware Fusion Player where the host was running Catalina. After creating the Install OS X El Capitan application in the Big Sur virtual machine, I would copy the Install OS X El Capitan application to the Big Sur host before following these instructions: How to create a bootable installer for macOS.

An alternative would to follow these instructions to create a bootable USB Snow Leopard installer. After installing Snow Leopard on the 2008 MacBook Pro, install the Mac OS X 10.6.8 Update Combo v1.1. Finally, use the 2008 MacBook Pro to create the Install OS X El Capitan application. You will need to use your Mac to do all the downloading.