Just a disclaimer that I’m not much of a expert or anything, or IT pro as you say also. Don’t have or ever used a mini v2, or pureboot for that matter.
Well my first instinct without telling you to look at qubes documentation would be to check and adjust xen configuration - confirm iommu, and all virtualization options are enabled and functioning still. For example maybe SMT, vt-x, iommu, etc; was disabled on this cpu, or from bios? TBH SMT(hyperthreading) is probably the most likely candidate of something being disabled and not throwing some sort of error, and leading to increased cpu usage. So also while you are doing that check dom0 cpu/ram allocation and adjust. I don’t know what will automatically change when you try to load a full qubes backup os on to different hardware but I’m will to bet you are going to adjust some things if you havent already.
Newer isn’t always better(especially on linux) for example: Lots of trouble running a AMD/Ryzen platform on Qubes when that hardware was new. Also you might have more ram capacity but what speed was your old ram? Though not sure if it matters much on a intel system but amd systems have a huge impact from ram timings and speed. Was the old system iGPU or stand alone GPU? etc. However the specs of the mini v2 seem good so I’m thinking it might be some specific settings.
Worst case you could reinstall Qubes on the new hardware and backup/restore the VMs. Though I haven’t done anything with qubes backup/restore functions to this date so take that with a grain of salt.