Having trouble with the volume from my iPhone 11 when exporting from iMovie to YouTube

I upgraded to the iPhone 11 to make better quality videos for YouTube, however I am having volume issues. When I upload my videos to iMovie and play them on the Mac the volume is fine, but by the time I have exported the edited video to YouTube the volume is so low that you have to have the volume on your device turned all the way up for it to sound like a normal level. If I increase the volume in iMovie before exporting it distorts the sound in YouTube. I purchased a Rode VideoMic Me-L but it appears to make matters worse as the volume is very low even in iMovie and I have to bring it right up to even hear it - I have contacted Rode separately to ask if the mic is faulty or not being used correctly as there are no settings I can change.

Anyone have any advice for me? TIA.