Anyone running an ETH validator node on a Mac?

Or know anyone that has?

I want to start staking but stubbornly can’t bring myself to buy a PC. 

I can’t be the only one.

Working on photogrammetry-3D - linux addict - Cosmos lover

Why not good? Inherent issues with keeping Macs on all day?

I also want to help diversification of hardware and OS on the network

Do you want your Mac be running 24/7 ?
Not good imo.
You should buy a NUC instead.

I want to help decentralise the network in my own little way, rather than join a pool.

it needs uptime, in your case best to join a pool

Make sure it has enough storage, you  should have 2TB SSD to budget for chain growth. External SSD is likely too slow, and with Macs it's harder to just open it up and pop in another M.2 b/c Apple doesn't believe in freedom.