How get three monitors work?

I know I'm a dinosaur, but bear with me.

Previous computer, Mac Pro (not Macbook Pro) 5.1. Two monitors plus TV via HDMI hooked up. No probs. System preferences/Displays got them, all three, and I could e.g. mirror one of the monitors to the HDMI-attached TV.

"New" computer, Mac Mini https://everymac.com/systems/apple/mac_mini/specs/mac-mini-core-i7-3.0-late-2014-specs.html no way achieving the same. Two monitors via mini-display works fine. But when pluggin in HDMI to the TV, one of the monitors goes black.

Why?

I'm an old fart. Started working with Apple/Mac 1992. Well aware how Apple has gone from "free spirit" to "lock our users down" the past decade, I'm still baffled that a pretty basic, simple feature was OK 2010 but deemed "superfluous" 2014.

Sorry for rant. But how can I make three monitors work? Two through mini-display output, one through HDMI?