Welcome to the Forum, @monica_kraus! 
I’ll start by saying that I haven’t yet updated to the v3.1 app (largely because Wyze does stuff like this, so I have auto-update disabled for the Wyze app in Google Play Store), so I can’t say with any certainty that the process I outlined above will work with this specific app version, but the app version should be irrelevant, and those steps should work for pretty much any app’s notifications in Android, provided that you’re using real Android and not something funky like OxygenOS.
I suspect that this response from Support is not accurate (I’m not saying that I don’t trust your reporting; I’m saying that I think Support may have given you inaccurate information), because this doesn’t jibe with my experience using Android in general.
First of all, the Forum is primarily a user-to-user community, so it’s kind of nice that Support recognizes the value provided by other users here, in a way, but I hope they’re not just foisting your issue off to another platform when they can’t resolve it directly. Second, if Wyze actually did manage to disable any ability for custom alerts, though (which I don’t know how they could do at the Android OS-level of notification management), then there actually is a Wishlist collecting suggestions related to future development of the v3 app:
If you poke around or use the Forum’s search feature, you can also find Wishlist topics related to notifications specifically.
Lastly, if nothing suggested so far is working for you, then you could look into third-party apps like Zedge for managing notification sounds. (I imagine there are others, and I’ve never used that one myself; I just know it’s one that some family members have used with good results.)