Question about RØDE smartLav+

Hello and thank you for your question.
Looking closer and doing some research on various websites, it appears that a USB-C > Jack 3.5 adapter does NOT necessarily support the functionality of an external lapel microphone.
It would be interesting to: see:
a) if your USB-C > 3.5 jack adapter is TRRS and therefore SmartLAV+ compatible
b) if the smartphone delivers a DC voltage of about 1.5 volts to bias the microphone
c) if there are options to set on the camera application of your Oneplus 7t (I'm on IOS with the Filmic Pro application) and there are possibilities to select the microphone connected to the jack port.
I know there are microphones with a USB connector, which require a USB-C On-The-Go adapter, but I digress.
According to a post on the Oneplus website, it's quoted that the camera's native app doesn't allow recording an external mic, but the article is from 2017, I don't know if your smartphone is newer.
Feel free to check out YouTube and Google for inspiration.
I hope I have been able to help you.
Best regards,

Jean-Michel