I usually set up a sub-flow and use it wherever needed.
The sub-flow accepts a single input: a requested item reference.
The logic is to execute a loop that contains a Look Up Record (not Records!) action, and a Wait for Condition action.
The key is to configure the Look Up Record action so that it does not fail on error (if no record is found) and the "loop until" condition as Look Up Record.Status is "Error".
In each loop, a single active Catalog Task is looked up.
If as a result of the lookup the Status property of the Look Up Record is "Success" (a record has been found) then the Wait for Condition is executed with the condition "Found Catalog Task Active is false".
At this point the Flow will wait for the Catalog Task found to be closed.
After the Catalog Task is closed, the "loop until" condition is evaluated, and will not be fulfilled (the last lookup record Status was "Success") so the loop will be executed once more.
A new lookup happens and if a Catalog Task is still running, it will be found a new wait will be executed.
If on the other hand the lookup finds no Catalog Task, the Status property of the Look Up Record will be "Error" (so not "Success"), the Flow will thus not enter the Wait for Condition action and will move to evaluating the "loop until" condition which this time will be fulfilled so the flow exits.
Thus if this sub-flow is called right before setting stage to "Completed" (at the end of the flow), it will allow holding up the main Flow as long as there is one active Catalog Task, no matter who or how that Catalog Task might have been attached to the Requested Item.
(The flow variable in the picture is just the sys_id of the Requested Item passed in as sub-flow parameter - not really needed.)
