I highly recommend Ecobee if you want an alternative to Google Nest.
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Since it's Homekit compatible though, you can go that route. HA easily discovers anything HK compatible as soon as you connect it to your network. So you connect Ecobee to HA with the HomeKit protocol in lieu of connecting it with Apple's stuff.
[1] ...and anything's better than the asinine on-device UI that Ecobee "updated" to a couple years ago (ask yourself: what would a foolish inexperienced "uX dEsIgNeR" do to ruin a plain old thermostat UI? It's that.)