Can't install MacOS on 2018 MacBook Pro
The school I support received at 2018 (Intel) MBPro as a donation. It had been updated to Ventura, but for various reasons, our school wants our laptops to be on Monterey. So I booted into Recovery Mode, opened the Startup Security Utility, and turned external booting on and turned the security to Medium. Then I erased the hard drive, and since Recovery only gives me Ventura as an option, I plugged in my trusty Monterey flash drive installer, but it refused to see that as a startup disk. I also plugged in my bootable Big Sur SSD, but it didn't recognize that either.
If I restart with the Monterey flash drive plugged in, holding the Option key, I get the 'Install MacOS Monterey' as a choice however when I choose it, it goes into Internet Recovery mode asking to connect to a WiFi network (why since the installer is already present?) So, I connect to WiFi and it takes about 20 minutes of processing to figure out that I need a web URL pointing to some basics about Apple Support and an error code -2005F
Looking that error up, some have solved this with zapping the PRAM and/or SMC, but neither has fixed this, on this laptop.
If I hold down the Option key with my Big Sur SSD plugged in, it lets me choose it, but then immediately goes into asking to connect the network, and 20 minute delay until failure -- same as above.
If it startup in target disk mode, and plug it into my main laptop, it says the destination is not accessible in Target disk mode.
If I boot into recovery mode, to open up the Startup Security Utility, it says that I don't have an admin account (true), so it can't be opened.
After all this, if I boot into "normal" Recovery Mode (command R) it immediately goes to Internet Recovery, offers me High Sierra, spins for a few minutes, and says that it can't find a server (presumably Apple no longer offers High Sierra internet recovery).
How do I steer around all of these roadblocks? Is there a way to do so that it doesn't end up on Ventura?