After announcing Windows 11 SE, Microsoft released some documentation describing the OS. It was discovered that there's no going back once you remove Windows 11 SE and replace it with Windows 11.
ExtremeTech spotted the documentation, and it reads, "...if you'd like to use a Windows 11 SE device for personal use, you may purchase a license for the version of Windows you'd like, completely erase all the data, files, settings, favorites, and the Windows 11 SE operating system on your device, and install your licensed version of Windows. After that, there would be no way to get back to Windows 11 SE."
If you were to purchase the affordable Surface Laptop SE (which is meant for education users), you could buy a Windows 11 license and install it. However, once you do, you can't go back to Windows 11 SE again, so if Windows 11 doesn't run well on your Surface Laptop SE (or other devices with Windows 11 SE), you're stuck.
There may be an option to reinstall Windows 11 SE through a recovery partition, but we'd need to test that ourselves to see if it works.
Basically, Microsoft is making it so only new devices can get Windows 11 SE. You can't download and install it after the fact---you must purchase a computer with it preinstalled. So if you have an older computer running Windows 11 and you think it would run better with Windows 11 SE, there's no way for you to get it.
With all that said, this is an OS that's meant for education users and not individuals, so none of this should be too surprising. If a school purchased many Surface Laptop SE devices, there's no reason anyone would need to mess with the operating system.
This is similar to Microsoft's policy with Windows 10 S Mode, so again, it's not particularly surprising.