I found the solution and fixed it:
It turned out that in Xbox Insider Hub
I somehow in the past had joined the PC Gaming previews!
(I was not aware of this)
So, I just quit PC Gaming preview, hence NOW, only Join appears:
And after installing Gaming Services from the MS Store, version 29.103.2001.0 got installed.
So, since 15 July 2025:
- if part of PC Gaming preview, the MS Store installs version 30.103.10001.0
- if NOT part of PC Gaming preview, the MS Store installs version 29.103.2001.0
Before 15 July 2025, the MS Store would NOT install version 30.103.10001.0; it would install version 29.103.2001.0.