Windows 11 and 10 installed

[Juliper]

I just changed to Windows 11 and so far it's great but I need to choose between Windows 10 and Windows 11 on every startup.

 

Why is Windows 10 installed anyway? And does it take valuable space in my SSD?

 

And how does I turn off this "selection menu"?

[Madsyrn]

here is a nice tutorial. Worked for me (the same method) for win 10 and ubuntu.

How to Dual Boot Windows 10 and Windows 11 | PCMag

[Oshino Shinobu]

You have an active Windows 10 installation somewhere, either on the same drive in a different partition or on a different drive. You need to delete the Windows 10 installation