This extension is free / Pay What you Want on DMsGuild. It is 5e specific and compatible with Unity and Classic.

https://www.dmsguild.com/product/328...iate_id=712946

This extension adds a few extra buttons to the desktop modifier buttons and moves the dice starting position.
The buttons added are the ones defined on the Modifiers window.
Attack:
Opportunity, Cover, Sup. Cover

Damage:
Critical, Max, Half

There are two versions of the extension, A and B. The difference is in the layout as seen below.