Making "Utility" Volumes for Fixing Macs

The TL:DR; of this question is, is an installation of macOS universal in the sense that if its on a USB drive, you can boot any compatible Mac off of it? AND separate from that, is the install universal in the sense that either an intel Mac or an ARM Mac can boot it?

LONG AGO, in a Mac ecosystem far far away....

You could use a Firewire cable and Target Disk Mode to diagnose a Mac with problems. It worked great in the PPC days. New OSes didn't come out all that often.

But then Apple killed Firewire. This was bad. But then I set up a Netboot server on my laptop. While this method was generally slower than a firewire boot, it had several advantages. I could plug into someone's network and boot multiple computers at once off of utility volumes I made ahead of time. And I could run netboot AND netinstall volumes for every single OS from 10.3 Panther all the way up to 10.12 Sierra.

But alas, anything that works good, apple's gotta kill it. So with 10.13, no more netboot. 10.13 is the last OS you can run a netboot server on, but 10.12 is the last OS that can BE netbooted.

Now you have to do things the worst way possible, by making utility volumes on a USB drive. So I got myself a 2 TB SSD and made a whole bunch of APFS volumes on it. With utility volumes for 10.14 up to 14 Sonoma. Its such a worse way to do it than netbooting, but if it's the only way, it's the only way.

BUT even this is NOT working!! One by one I installed the OSes using a 2018 Mac mini with the USB SSD plugged in. Now I'm off to a customer's house with my drive. I plug it in to a 2019 iMac and only Mojave and Catalina (14,15) would boot. Every other newer version gave me the ol' circle with a line through it.

So what the heck is going on? What does apple want you to do here? I know they want Macs to be throw-away, disposable appliances, but I'm really fighting that as much as possible. But Apple sure isn't making it easy. Is there any other method for diagnosing that I'm not aware of? Its not enough to boot into internet restore, I really need to boot into a working full macos installation.