I live in Canada. My girlfriend is Chinese (also living in Canada), and while we are able to communicate via SMS, her mobile carrier isn't the best, and so there have often been issues for us with regular texting. She expressed a strong preference to use WeChat, at least as a backup option for when texting fails us. While I have some pretty significant reservations, it's not the hill I want to die on. So my question is: what can be done to use WeChat without compromising my whole phone? I'm okay with it if our conversations aren't private, but I'd like to know that I'm not giving unfettered access to all of my phone's systems and data to the CCP. What can be done to limit the reach of this ubiquitous app on my device?
You can put it in a work profile and trust that Android is protective enough to keep your data safe and access limited. Otherwise buy a second phone just to put WeChat on it. Don't know how WeChat works, but if it's like Whatsapp then you don't need to bother with a secondary number.
Basically 2 options: A work profile or a separate Android user profile. I'd definitely recommend the latter, as it has much stronger isolation. Some vendors like Samsung disable user profile support though. A work profile is still better than nothing.
Probably not the solution that you are looking for, but maybe try Signal? It's better than SMS, WeChat, WhatsApp and most other messengers. Unlike stuff like WhatsApp and SMS, Signal can even be used in China, because it has a built-in censorship circumvention system which uses special TLS proxies or can even be used over Tor.
This feature only exists, because the people behind Signal actually care about freedom and want to help their users. Unlike WeChat, Signal is not built by any government to spy on people, and unlike commercial messengers like WhatsApp and Facebook Messenger, it's not built by a corporation that wants to extract money from their users by selling their data. It's a non-profit organization, created by people who are dedicated to make the world more private and secure. Just keep that in mind when choosing a messaging app.
That's an oxymoron. Apart from having a dedicated device, you can't really sandbox the app since it requires basic permissions to function that give access to core phone functions. See https://reports.exodus-privacy.eu.org/en/reports/com.tencent.mm/latest/
You can try to limit permissions of some features that you don't intend to use.
If you actually bothered to read, you would know that it shows 0 trackers because Facebook doesn't embed their trackers in the SDK, and inject them later once you grant them the permissions to the device, exactly the same way WeChat does.
Use your phone's permission system, look at the app's permissions, and set them as strict as the app will allow you to while continuing to function. I don't see any particularly scary permissions that aren't optional (looking in Google Play/the Android permissions set).
Pretty much anything beyond that you're wasting your time unless you want to carry two phones.
Edit: I see you went with Shelter; hadn't heard of that either. Probably overkill, but as long as it doesn't cause problems/the app works for you, go for it.
Well it means that if I do grant a permission to the app like for example file storage access to send my gf a funny meme I downloaded, it doesn't get access to all of the pictures and files on my device.