Why only Windows 11 23H2 is available? Not the 24H2

If the Windows Upgrade Assistant is only offering you the 23H2 update instead of the latest 24H2, it could be due to several reasons. Microsoft often releases feature updates in stages, prioritizing stability and performance, so not all devices receive the latest update at the same time. Your device might not meet certain prerequisites for the 24H2 update, such as hardware compatibility or specific software configurations. Additionally, the rollout may still be in progress, and availability can vary based on geographic region or the specific Windows version you’re currently running. You can check for updates manually via Settings > Update & Security > Windows Update, or consider waiting a little longer for the broader rollout of 24H2.

Most probably your PC does not meet certain system requirements of Windows 11 24H2.

Lack of bandwith. bits and bytes, /etc

Make sure your device meets all Windows 11 primary requirements:

https://www.microsoft.com/en-in/windows/windows-11-specifications?r=1

If your device meets all requirements, try upgrading via Windows 11 24H2 ISO file:

https://www.kapilarya.com/how-to-upgrade-to-windows-11-version-24h2#method-2-upgrade-to-24h2-from-iso-file

Let us know if this helps! 

Note: Included link in this reply refers to blog by a trusted Microsoft MVP.