One of the things that FLATTEN does is undo a layer of nesting of a list, such as the output of split(Monitoring, " \| "). Note that you probably want spaces on both sides of your separator in that split since "FundA<space>" and "FundA" are not equal.
So changing the last line of your starting code:
FLATTEN split(Monitoring, " \| ") AS "Monitored"
WHERE contains(Monitored[0], "FundA")
Then you can change the column definitions in the top of your query to
Monitored[0] AS "Fund",
Monitored[1] AS "Action Item"
Note that I just made up the name “Monitored” for what to call the result of the split operation - you can call it whatever, just change it everywhere it is used.
Does this allow the “WHERE” to work?
Another note: if you use GROUP BY you’ll want to get rid of the “without id” on your table to actually see the funds, at least while you are trying to make sure everything is working!
Good luck!