Hi there MartinG8hR,
Thanks for joining us in Apple Support Communities! We understand the iTunes Remote app on your iPhone is having difficulty accessing your media library on your Mac. We're glad you're here, and we can provide some guidance.
To start, you mentioned your iPhone is running iOS 14.4.1, which is currently outdated. We'd suggest backing up and updating to iOS 14.6, which is the latest software version. If needed, this link provides step-by-step instructions for updating your iPhone:
Update your iPhone, iPad, or iPod touch
If the issue persists after updating your iPhone, let's make sure you're following the steps in the link below to set up the iTunes Remote app:
Set up the iTunes Remote app for Music on Mac
Let us know how it goes.
Cheers.