We don't yet support running ios and android apps directly under .NET 6 with platform-specific frameworks, because to support that we had to wait for Microsoft to release .NET Maui, and MAUI was released just 8 days ago. (see Productivity comes to .NET MAUI in Visual Studio 2022 - .NET Blog )
Right now, the way to have it working is using Xamarin apps, which is what we currently support. But we are working as I write this in supporting the new .NET 6 platform-specific frameworks, we should have a release supporting it in the coming weeks.
From what I saw on your apps, the iOS app fails because it can't start SkiaSharp (which probably doesn't support the new platform-specific frameworks either) and the Android app fails because it can't find any font (and the android-specific ways to find fonts aren't compiled in the .net dll in the nuget package).
The idea is to provide FlexCel dlls that don't require skiasharp at all, but for that we needed support from frameworks that hadn't been released yet.