A note about my current HP EliteDesk 800 G5 Mini configuration that may help others:
I am careful about maintaining a fully operational production baseline for my G5 Mini. This means that I test OC config changes, new OC versions and macOS updates BEFORE I introduce the changes to my production environment.
I have completely ditched Windows on my G5 Mini and operate with two M.2 NVMe SSDs (Western Digital Black) for macOS.
I keep my working OC baseline on one of my NVMe SSDs and first make OC changes on a USB, so that I can easily boot my rig if I accidentally screw up the EFI on the USB. After verifying the OC changes on the USB, I backup the current production OC EFI and then transfer the USB EFI (with OC updates) to the NVMe SSD EFI. I maintain backups of all of my old EFIs.
One NVMe SSD has my production macOS baseline and the other M.2 NVMe SSD is my macOS test environment. My current production macOS is Catalina and I'm testing Big Sur 11.4 with the apps / functions that I need.
When I am satisfied that Big Sur is ready for production (for me), I'll clone my production macOS volume to the test volume and then upgrade the test volume to Big Sur. After more testing, my Big Sur volume will become my production volume and I'll change my Catalina volume (the former production volume) to my test volume (e.g. for testing Monterey).
On top of the two M.2 NVMe SSDs, I have installed a 2TB 2.5" SATA HD (see
here) on which I maintain backups and TimeMachine (only using TimeMachine for the production volume).