Unclear if you're saying voice input doesn't work or if Google assistant can't access your SMS.
I'll try to address both:
Make sure you have the Google speech recognition & Synthesis app installed from the Play store.
Google maps and the Google app should also be installed from the Play store. I believe you need to be logged into a Google account for these voice features to work.
You need to also make Google your default assistant app in that profile. Go to Settings -> Apps -> Default Apps. This will also allow Google assistent to pop up if you hold down the home button.
You need to also set Google speech recognition & synthesis as your voice input and text-to-speech app. Go to Settings -> System -> Language. Even if it appears selected, it may not be enabled to work yet. If you can't change the pitch and speed, it's not working yet. Actually click on speech recognition (not obvious) to enter settings. You should be able to download additional voices. The app doesn't need network access after you download voices.
In the app settings for google speech recognition & synthesis, make sure it has access to microphone always and allow it to draw over other apps, which appears to be necessary to work with Google Assistant and Google maps.
For Google, give it access to your microphone, network, sms, and anything else you believe to be useful. For example, if you want to ask Google assistant for directions to feed to Google maps, it will likely need location.
You will not have Hey Google functionality, but you should still be able to access Google Assistant by holding your home button or selecting the Assistant microphone button while in navigation mode in Google maps.
Maps should also have similar permissions. Sensors are also necessary for compass directions and physical activity and storage is necessary for Timeline features if you choose to use those.
Android auto will similarly need microphone permissions and other permissions you want to give it.
Given the number of permissions, some choose to isolate this stuff to a separate user profile.
If you can not make phone calls or see SMS, make sure the profile has phone/SMS access on manage users setting on the owner profile. Also make sure you gave each necessary app phone/SMS permissions. And on the android auto user profile, go to Settings -> apps -> sandboxed Play services -> Android Auto, you need to select the necessary toggles for things to be allowed through.
If you're looking for more privacy respecting alternatives, you can substitute Google maps with Organic Maps or Magic Earth. Magic Earth has built-in text to speech that will read directions to you, but for Organic Maps, you can install RHVoice, download one of the voices, and enable it in your voice input/TTS settings similar to how I explained it above for the Google speech recognition & synthesis app.
You will lose Google Assistant. But you can install another voice input app like FUTO Voice to avoid manually typing addresses. FUTO Voice can be activated on your keyboard and by using the microphone button that appears in Organic maps.