I’ve had a very good experience using one of these to provide HomeKit compatibility to Nest devices: https://www.starlinghome.io
[1] https://www.npmjs.com/package/homebridge-nest [2] https://github.com/homebridge/homebridge
I need to run Homebridge anyway for a bunch of devices that I want to be available via Alexa and HomeKit, so for me there was no incremental complexity. I'm running Homebridge via a Docker image[1] on my NAS (using QNAP Container Station), with Homebridge UI to manage.