The verdict

CPU
HP Elite Mini 800 G9 has 4.1x the CPU throughput (16,372 vs 4,000 PassMark).
Plex
HP Elite Mini 800 G9 transcodes more 4K HDR streams (~5 vs ~4).
Idle power
HP Elite Mini 800 G9 idles lower (5W vs 14W) - cheaper to run 24/7.
Networking
QNAP TS-464 has more NICs (2 vs 1) - better for a firewall or VLAN trunk.
RAM ceiling
HP Elite Mini 800 G9 takes more RAM (64GB vs 16GB).
Local AI
QNAP TS-464 has a PCIe slot for a low-profile GPU - the other needs a DIY build for local LLMs.

Which wins for each job

Job HP Elite Mini 800 G9 QNAP TS-464
Plex / Jellyfin ~5 streams win ~4 streams
Frigate NVR ~4 cameras ~4 cameras
Proxmox / VMs 16,372 PassMark win 4,000 PassMark
Firewall / router 1 NICs 2 NICs win
Local AI / LLM no slot PCIe GPU slot win

Approximate - capacity estimates from curated specs, the same logic as the recommender. Verify against your exact setup. Prices move; check the retailer.

Full specs

Spec HP Elite Mini 800 G9 QNAP TS-464
Price (list) $550 $549
CPU Intel Core i5-12500T Intel Celeron N5095
Cores / threads 6 4
PassMark 16,372 4,000
iGPU UHD 770 Intel UHD (16 EU)
NICs 1 2
NIC model Intel I219-LM Intel I225-V
RAM max (GB) 64 16
M.2 free 1 2
PCIe slot none x4
Idle (W) 5 14
TDP (W) 35 15