Hi @RichardWei. Unfortunately the beta program is closed for the ArcGIS Runtime SDK for Qt on embedded Linux. We can't offer any official support for it since it was never moved into production.
That being said, I'm excited you want to run on Raspberry Pi. That was my initial goal with the entire program!
I can share a few things with you that may help you get a bit further, but ultimately I do not think it will work.
>Is it possible that there is a lack of implementation of the 2D map in this beta SDK?
It is there and implemented. This is perhaps the biggest weak spot of the Beta. The Beta requires full desktop-class OpenGL support; not OpenGL ES. I don't know if such support exists on the Pi 4, but this could be the issue. Our main test devices were higher-end Nvidia devices, like the Jetson TX2 and Jetson mini. Furthermore, it requires hardware GPU drivers; not mesa rendering in software. The Pi 4 may have this but I'm not certain.
>This would lead me to believe that there is no basemap in this beta SDK for Arm. Would I be correct?
It's all there. All the binaries are present but the workflow might change if you are cross-compiling from one target or compiling natively on the Pi itself.
Another potential complication is the Raspberry Pi OS. They're just recently rolling our 64-bit OS support. This is worth mentioning because the Beta only supports 64-bit (aarch64-linux-gnu) targets, so that means the OS must be 64-bit as well. It's not enough that the PI is 64-bit hardware but still running the 32-bit Raspberry Pi OS (or Raspbian). It sounds like you do have this already, but it is worth mentioning.
I hope this helps you out, but since the beta program is closed we are limited in how much we can troubleshoot.
Good luck!