Android Studio's Properties Window Missing

That's because of the Component Tree's size which is too much.

See, before increasing the size:

After that:

Try to decrease the size with clicking and holding the click from left side of that panel to right.

This will solve the problem.

Reduce the size of the Component tree panel will solve your problem.

For a better solution, you can click on panel option, In editor mode, Left. And restart and change position of the panel to Right. (solve the problem on my computer). This problem is only present when the properties panel is attach to the right sidebar

This worked

Select design view from layout editor.