I am in the same boat as you, Google broke Assistant very slowly over the last year or more. I mainly used it for navigation when in the car, or on a bike, and when at home to control various “smart switchs” and other IoT devices.

Its been a pain TBH, but its kind of helped with my slow de-googleing of products and services I use. Though like you said this could essentially become a hobby as there is no one fit-all alternatives.

I have yet thought to find a way to replace voice Navigation in any of my alternative Map apps, but most of everything else has been replaced slowly.

Where I would suggest starting is looking at this video as a example of what’s possible with Local Assistants and models.

www.youtube.com/watch?v=ZxjuEHTKXMw

(You don’t need the fancy “robot” shown in the video but you do need mic’s and speakers for voice controls around a house. You can also use your phone though)

If you do “smart home stuff” look into HomeAssistant and the various integrations for voice controls. Home Assistant also has something called Music Assistant where you can integrate your Spotify and local music library, then with voice commands you can request certain tracks ve played.

HomeAssistant basically becomes your “unified environment of services” where everything becomes “integrated together”. Things like smart switches, your calanders, notes, weather forecasts, music, presence detection, so now you can ask your voice assistant questions and get responses like the weather is sunny, or the kid is home.