How I can certify my new driver with HLK for Windows Iot?

I am preparing a setup for HLK testing on Windows 10 x64 IoT Enterprise 2022 LTSC for my new developed driver.
I installed HLK testbench for Windows 10 2004 on a Windows Server 2016 like for testing desktop systems on Windows 10 2004, 21H2 or 22H2. Windows 10 x64 IoT Enterprise LTSC 2022 I installed.on a desktop computer. Firewall for domain, public and private network I disabled here and installed test client from server (out of the directory HLKInstall\Client). I installed my device for testing and moved the test client in a separate MachinePool in HLKManager. I created a new project in HLKStudio, selected the MachinePool and my device under test. Up to this point all everything is as expected and known from testing on desktop operating systems. Now the problems:

1. In tab 'Tests' I can see many tests but if I load the newest playlist 'HLK Version 2004 CompatPlaylist x86 x64 ARM64.xml' all tests are skipped and the tab is empty. Am I using a wrong playlist or have anyone an idea where the mistake is?
2. So I started with testing without a loaded playlist. My device and driver can pass all listed tests in this case. So I created a submission pakage with driver and driver symbols. This package I signed with our ev certificate which is deposited on Microsoft Dashboard. Nevertheless uploading of the signed submission package fails with unspecific error message: 'One or more errors occurred.' There is no hint what the problem is. Has anyone an idea for this?

Based on these problems, the question arises as to whether testing under Windows 10 x64 IoT Enterprise 2022 LTSC (or IoT systems in general) is even possible. If you then take into account the observation that drivers that have been tested for the desktop system W10 22H2 and published on Windows Update also load under Windows 10 x64 IoT Enterprise 2022 LTSC, it is questionable how useful testing on IoT is. Is this perhaps even the right way and the way intended by Microsoft to carry out the tests on the corresponding desktop system?

Can anyone help me or give me a hint what to do?