Hai @icontre1 Yes, this is a known issue for all adobe analytics customers and I believe same in GA4 as well.
If this dimension is really needed for you to understand few important customer journey behaviors, I would suggest few of the below option,
1. Create one custom traffic variable or conversion variable to track the mobile device using the feasible option to identify the mobile device - you need to work with your app developer for better solution
2. Breakdown the Mobile device data set by Browsers as shown below, you can find the what works and what not works in your website on those browsers.
Any functionality is most affected by browsers so we usually rely very less on the mobile device dimension.
Hope this is helpful for you.
I also went through one thread but that is not giving any solution
https://experienceleaguecommunities.adobe.com/t5/adobe-analytics-questions/mobile-device-going-into-...
Regards,
Bala