I have added PowerShell 7.0.3 to Wimbuilder as a standalone plugin/app. (Not a preview version)
PSVersion 7.0.3
PSEditon Core
GitCommitId 7.0.3
OS Microsoft Windows 10.0.19041
Platform Win32NT
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0
It is built from MSMG PEPacks for Microsoft Windows (10.0.19041.84,x64,en-US)
It is not suffering from executing native commands.
Working= reg, regedit, diskpart, notepad, mspaint, cmd, etc.
If you like, I can share or even help you troubleshoot with this issue,
beings I have a working PS7 install.
Regards
RoyM