normally you can mark nearly all variables as retain, even when they're an input to a FB or FC.
But you've keep in mind when you're using a global Variable that the option is only available in the global Variable sheet.
In the local Variable sheet the Variable is than marked as "Var_External" (somekind of pointer to the global with the same name) and all options are grey.
In case this is not the solution I need to know more about the application, maybe a screenshot of the variable may help.
Of course you can call also our free automation hotline +4952819462888
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