Critical damage after a specific dice value

In the form we use in my game, there is no pre-programmed calculation for critical damage. Is there a way to do this in the same macro together with the hit? I know there is a marker cs> which serves as an indicator of when the damage will be critical, but is it possible to use this to add a multiplier to the damage roll? since the critic in the critic of my game is to multiply the damage rolled by 2 or by 3 is there a possibility to use this as an if to perform the damage multiplication or not? please help a friend who is starting to venture into this wonderful world and wants to improve their gaming experience

Unfortunately this needs to be either supported by the sheet, written into a custom sheet (Pro) or done with API (also Pro). Some sheets, like the 5e one, do handle this functionality but it doesn't sound like yours does. The best you can do with vanilla macros is to use the cs and cf markers on the die roll, then manually choose whether to roll normal or crit damage with a query or with a choice of macros.

and there is also no possibility to create a variable to store the damage and thus use the value the value at another time within the macro right? If that would serve to at least present the two values

That's correct - there's no way to store a roll's result for later use. You can display  a roll later, but you cant use it in further calculations.