There is no way for me to check this app....
Fiddled a bit more and took note of what changed from 12.0 to 12.5.
It seems on 12.5, MIUI now scans every app that is being installed by default. I am assuming this app scanning process takes liberty in preventing certain apps from executing certain system actions.
Would've at least been nice after the app scan to have a pop-up notification telling me what the app will be capable of doing in the system (such as initiating SMS messages), or what MIUI will henceforth prevent the app from doing. Then MIUI could let the user decide whether or not to enable the recommended security measure.
I also think it's confusing. On one hand, the user may grant permission for the app to execute SMS operations. But on the other hand, MIUI's Security settings can override the granted permission anyway?
The workaround I found is to turn off the app installation scanning from the Security settings and then I reinstall the app.
Bypassing the scan, the app would then finally proceed in letting me choose from what SIM would I like it to send a verification SMS through. And then it proceeds with automatically sending an SMS.
I don't think the MIUI Security scan should be overriding or negating user-granted permissions. I am not sure sure if it's a bug, but I think the issue lies in what looks like an app security policy conflict.
Lastly, it seems redundant to have another Security scan for apps being installed through the Play Store. Couldn't this be enabled just for direct APK installs by default since Play Store installations are already secure?