Hi Radoslaw Kubas,
Greetings from Syncfusion.
Currently, we are supporting minimum version of Xamarin.Forms is 3.6.0.344457. So, few dependencies are not referred from AndroidX when you work in Xamarin.Forms 4.5 and above. So, you need to refer those assemblies manually. Also, we would like to inform that we have planning (Still checking some feasibility) to upgrade minimum Xamarin.Forms Support version on volume 3 main release.
We suggest you to add Xamarin.Android.Support.v7.RecycleView package in Android project manually to resolve the reported issue.
Please let us know , if you have any other queries.
Regards,
Sakthivel P.