No "ins" key

Go to Add | Measures | Insert One Measure.

You can also change the keyboard shortcut:

1. Go to Edit | Preferences…
2. Switch to the Shortcuts tab/
3. In the Search box, type “Insert one measure”.
4. Select “Insert one measure” in the list, then click Define… and press the new keyboard shortcut.
5. Click Add (or Replace, if you want to keep Ins for some reason), then click OK.

Pretty much any keyboard that lacks this key would provide a build-in shortcut for it, though. On one of my machines it is Fn+Delete, on another it is Fn+Period, etc.

But yeah, you can also customize the command within MuseScore.