> How are you checking whether it's there or not?

The desktop distribution of 3.9.8 is the most obvious case, since it causes sys.getwindowsversion() to report Windows 8.0 (6.2.9200):

    C:\Temp>"C:\Program Files\Python39\python.exe" -q
    >>> import sys
    >>> sys.getwindowsversion()
    sys.getwindowsversion(major=6, minor=2, build=9200, platform=2, service_pack='')

But I checked for the manifest directly using the SDK manifest tool, mt.exe. It's missing in 3.9.8:

    C:\Temp>set file=C:\Program Files\Python39\python.exe
    C:\Temp>mt -nologo -inputresource:"%file%";#1 -out:python.manifest
    mt : general error c101008c: Failed to read the manifest from the resource of file 
    "C:\Program Files\Python39\python.exe".
    The specified resource type cannot be found in the image file.

    C:\Temp>set file=C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.9_3.9.2288.0_x64__qbz5n2kfra8p0\python.exe
    C:\Temp>mt -nologo -inputresource:"%file%";#1 -out:python.manifest
    mt : general error c101008c: Failed to read the manifest from the resource of file
    "C:\Program Files\WindowsApps
       \PythonSoftwareFoundation.Python.3.9_3.9.2288.0_x64__qbz5n2kfra8p0
       \python.exe". 
    The specified resource type cannot be found in the image file.

For comparison, the manifest is present in 3.10, which was built over a month ago:

    C:\Temp>set file=C:\Program Files\Python310\python.exe
    C:\Temp>mt -nologo -inputresource:"%file%";#1 -out:python.manifest
    C:\Temp>findstr longPathAware python.manifest
          <longPathAware xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">true</longPathAware>

    C:\Temp>set file=C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.240.0_x64__qbz5n2kfra8p0\python.exe
    C:\Temp>mt -nologo -inputresource:"%file%";#1 -out:python.manifest
    C:\Temp>findstr longPathAware python.manifest
          <longPathAware xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">true</longPathAware>