It seems that the issue of app icons displaying as an arrow instead of the actual app icon may be related to the ongoing updates and changes in the Microsoft Store, especially for users in the Dev channel. Microsoft has been working on redesigning icons across their products, including updates to the Windows 10 and 11 icons. This could potentially lead to temporary inconsistencies in how icons are displayed after downloading apps.
If this issue persists, it might be helpful to check for any updates to the Microsoft Store app itself or report the issue through the Windows Insider feedback channels to ensure it is addressed in future updates.