Question about RØDE smartLav+ incl. SC3 adapter

I bought the RØDE smartLav+ mic last year for voice recording when I still had an iPhone 7. This year I bought a Huawei P20 Lite and I can also use the mic for voice recordings without any problems. Now I also want to record video with voice (VLogging) and here either the RØDE smartLav+ mic or the Huawei P20 Lite is failing. I don't understand why I can record voice but not video with voice. I spent all day yesterday googling for a solution. The internet suggests that this function is not enabled in the camera app supplied by Huawei. Why not? The Open Camera app is usually mentioned as a solution, but it doesn't work for me either. Without the microphone, I can record voice videos (in poor voice quality). With the external microphone, the video remains completely mute! At this point I feel really cheated! I just don't know yet from whom, Rode or Huawei? With all the accessories (adapter, windscreen, extension cable), I spent almost 117 Swiss francs on the RØDE smartLav+! With such an expensive device, can't you expect it to just work? What happened to good old plug and play? We're talking about a stinkin' standard jack plug here! Having vented my heart, I'll politely ask around if anyone knows any advice. Do I have to buy a new mobile phone now? Do I need a different microphone? Or is there perhaps a solution for my existing equipment? Thank you very much for your answers.