Had a similar problem and it was two things:

• The crank typically connects to an arm that slides along a metal bar as it opens/closes (sorry - probably using the wrong language). The metal bar may be so rusted that the arm cannot slide along. You can (as someone mentioned) take off the screen, unlock, turn the handle and push the window gently with your other hand to open. Once it’s open you can check that bar for rust. If seriously rusty unscrew that rusted bar, bathe in vinegar /scrub to clean it up.

• The gears in the crank had warn down to the point where they couldn’t generate enough force to open the window. I believe it’s called a window “operator”. Anderson window website can help you find the right operator. Replacing the operator means removing the bottom of the window frame and replacing the mechanism. Lots of YouTube videos helped me here.

Edit: noticed the brand in the photo

One other note: I also have a similar window that no longer opens because the wall was damaged/caused the frame to sag just enough to make opening the window impossible. Wall damage was caused by a poorly cared for outdoor shower directly outside.

Hope this helps!