Set this window flags Qt::Window | Qt::WindowTitleHint | Qt::CustomizeWindowHint

Note, that on some platforms it behaves in different way. For example on Mac OS X it Disables, (not hides) close/minimize/maximize buttons

You can do that using Windows themes, with which you may customize just about every aspect of Windows.

However, this is a complex subject, and creating themes as XML files is not for everyone, so using a third-party product is recommended.

Perhaps the best product in that area is Stardock WindowBlinds, which is however trialware (although not very costly).

This is expected and is how many GUI applications work in Ubuntu. You don't mention exactly which applications you are using, but from the screenshot, that one appears to be written using the GTK toolkit. GTK (a.k.a. Gnome) apps do not, by default, including a minimize or maximize icon in the window title area.

Other applications may use other toolkits. For instance, if you install xterm, you will see a minimize and maximize icon.

You can, however, add minimize and maximize controls to GTK apps by running:

gsettings set org.gnome.desktop.wm.preferences button-layout "close,minimize,maximize:"

See this answer for more details and options.

As for Ximg, that is an alternative way of running GUI applications in WSL. Under Windows 11, you don't typically need Ximg, since WSL2 includes the WSLg feature for running Ubuntu GUI applications.

However, if you do want to use Ximg, yes, you likely did miss a step. You would need to:

• Correctly set your DISPLAY environment variable to point to Ximg instead of WSLg:

  • Ximg: export DISPLAY=$(hostname).local:0
  • WSLg (the default): export DISPLAY=:0 (automatically configured)

• You'll also need to make sure your Windows firewall allows the connection from WSL2 to Windows (since WSL2 is actually on a separate virtual network). Using Windows Defender, you should normally see the "Allow" popup box the first time you use it, but if you miss it, you'll need to set it manually.