It has been quite a few years now, but, the Shields have not really changed at all, few OS updates, but nothing major. Apple keeps their product up-to-date and is making newer models. Nvidia, seems to have zero plans to make a newer modern hardware Shield TV, and the current model from 2019 is on Life Support essentially. I overall, see Android TV/Google TV to be a dying thing. Will not surprise me to see Google kill it off some point in the next few years.
To me, the Apple TV produced much better picture quality and audio quality. Is very subjective and also highly dependent on your specific hardware setup and environment and tastes.
Audio pass through...for those who want un-touched bitstream to go to a AV receiver, sure, Shield offers that.
Apple TV, now has a "Continuous Audio connection" setting that uses a Dolby MAT connection(which is PCM with Atmos metadata), but, no, there is no direct pass-through.
I do not use a AV reciever, instead, a Headphone DAC that connects a set of Creative 2.1 PC speakers. I do not care about fancy surround sound, and the downmixing Apple TV natively does and my hardware, sounds much better to my ears than the Shield ever did.
Video quality, also, is just cleaner and crisp. Apple seems to have better upscale processing compared to Nvidia's. The Shields "AI" upscaling just uses a edge sharpen mask filter and looks like crap on lower resolution video. I also have never found any video player app that comes close to Infuse Pro on Android. (well, bare MPV on Android is best for playback quality and codec support, but is barebones UI, directory tree navigation, and you need to manually setup config, very clunky)
Again, all is very subjective.
Use what works best for you.