I have Apple keyboard with numeric key pad attached over USB to WIN10. I'm invoking the INSERT using 2 different ways:

Method 1:

Switching numeric keypad off ( using "clear" button ) and then pressing "0" key. It does togle the state of the INSERT "key".

Method 2:

In "Start Menu" of the WIN10 I search for "On Screen Keyboard" and launch the on screen keyboard. Then simply set the state of INSERT key there.

There are exceptions to the behavior; but if the system is in its defaults with respect to the keyboard behavior or if the utilities/extension affecting the OS processing of the keyboard events are programmed correctly - it works reliably.

1. If you are remoting to a PC using CITRIX (or anything else) as it is stated in the question.

   In "Start Menu" of the WIN10/11 one can search for "On Screen Keyboard" and launch the on screen keyboard. Then simply set the state of INSERT key there.

2. In addition - if one is using the full size Apple keyboard ( with num keypad ) on WIN machine or runing a virtual WIN machine on MAC OS X

   Switching numeric keypad off ( using "clear" button ) and then pressing "0" key. It does togle the state of the INSERT "key".