I run WeChat on a separate phone with LineageOS and monitor its actions via the XPosed framework. It regularly scans my Wi-Fi network, checks the list of installed apps, randomly accesses sensors, and does plenty of other dubious things.

There was also a period of time where if you didn't give it Location permissions, it wouldn't let you login to WeChat. With LineageOS I was able to "give" it the permission but hand it fake sensor data instead of actual hardware data from the OS side.

I'd never think to run WeChat on a closed-source OS like iOS that doesn't give access to these kinds of introspection.

That said I don't necessarily think Facebook's or Google's set of apps are necessarily better in terms of spying, but at least it's possible to message people using a pure web interface without downloading anything, which WeChat doesn't let you do.