Hi Sibro,
I figured out what is missing and managed to work around the issue.
To install this app that is in the Apps folder it requires appinstaller that is also missing.
I let the MS store update itself to the latest level, then searched for appinstaller and installed it.
After that just clicking on the file below that was in the Apps folder created when the ISO was built, it installed the SecHealthUI at the level 1000.25115.1000.0_x64
Back in business, but that is quite ridiculous. 🤣🤣
Looks to me that something basic is missing in the clean install process or the way the ISO is built.
It needs to install appinstaller before it can install SecHealthUI .appx 😡