Updates 2022/1/3: See Update on App-V Sequencer Versions – Confessions of a Guru (tmurgent.com)
UPDATED FYI,
It seems that in the latest version of the ADK (21H1) requires an OS build that is newer than 21H1. It isn’t very clear in the documentation, but, at least for the sequencer, that version of the ADK requires an insider’s build (currently) for …

MSIX App Attach requires a format conversion from the standard msix file in order to attach the MSIX packages efficiently. This efficiency is important in non-persistent image scenarios like pooled VDI, as well as semi-persistent scenarios like shared multi-user operating system connections (Server Based Computing, like RDS/RDMI as well as multiuser Windows 10) as the end-user doesn’t want to wait …
Customers that use Microsoft App-V are certainly interested in the potential future of MSIX. While the compatibility levels for typical applications under MSIX is not yet acceptable overall and we will be continuing to leverage App-V for years (decades?) to come, I believe that it is important for them to begin the job of working with MSIX apps when we …