The verdict

CPU
Beelink SER6 Pro has 1.1x the CPU throughput (22,289 vs 20,168 PassMark).
Plex
Minisforum UH125 Pro transcodes more 4K HDR streams (~8 vs ~5).
Idle power
Minisforum UH125 Pro idles lower (10W vs 12W) - cheaper to run 24/7.
Networking
Minisforum UH125 Pro has more NICs (2 vs 1) - better for a firewall or VLAN trunk.
RAM ceiling
Minisforum UH125 Pro takes more RAM (96GB vs 64GB).

Which wins for each job

Job Beelink SER6 Pro Minisforum UH125 Pro
Plex / Jellyfin ~5 streams ~8 streams win
Frigate NVR add a detector ~6 cameras win
Proxmox / VMs 22,289 PassMark win 20,168 PassMark
Firewall / router 1 NICs 2 NICs win
Local AI / LLM no slot no slot

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 Beelink SER6 Pro Minisforum UH125 Pro
Price (list) $429 $439
CPU AMD Ryzen 7 7735HS Intel Core Ultra 5 125H
Cores / threads 8 14
PassMark 22,289 20,168
iGPU Radeon 680M Arc (Xe) Iris Xe class
NICs 1 2
NIC model Realtek RTL8125 Realtek RTL8126
RAM max (GB) 64 96
M.2 free 1 1
PCIe slot none none
Idle (W) 12 10
TDP (W) 54 28