I tested another scenario and it works (not sure if it will work all the time - need to follow up the performance).
I'm using a Data Table to show my records (around 1500 records so far) and I have separate Edit Form based on the selection from the Data Table. However, I filter the Data Table to show only the relevant data for the user which in this case is just below 500 records per selected filter (my delegable max records is set to be 500)
I added UpdateIf function in a separate save button connected to the edit form to update the Data Table.
When I tested records which are located between 1000-1500, the UpdateIf function works.
So Instead of having the Filter () and UpdateIf () once after another in the same formula bar, it might work best to separate it completely ( I haven't tested thoroughly and repeatedly with bigger records) and set the max number of records to show in the data table as just below the max delegable records.
I might think, if the filter and updateif function is placed once after another in the same formula bar, it might have the same effect like "ForAll" function as follow:
"..When writing your formula, keep in mind that records can be processed in any order and, when possible, in parallel..."
(that's why it might not work all the time? ) - again as you mentioned this has not been proven yet by the Microsoft and might not be reliable.