You're getting this message because of the nested expression
Filter(RRF, true)
You are filtering the data source, but the expression that you use does not reference any columns from it - this is usually an error, as that expression is equivalent to
RRF
If it is not an error in your part, then yes, you can ignore it.
There is another issue, however - if the number of items in your SP list starts growing, you may reach the delegation limit (the 'Max' function is not delegated (for more information on delegation, see this link). One way to work around this would be to sort the items based on your column in a descending way, and take the first element (which would be the higher):
First(SortByColumns(RRF, "RRFID", Descending)).'RRF ID' + 1
You may still see a delegation warning (that the 'First' function cannot be delegated to SharePoint), but that would be ok as it would apply to a sorted result.
Having said all that, I believe that SharePoint does have by default an auto-incremented id for items of its lists. The column "ID" is hidden, but you can show it in your sharepoint list (and access it from Power Apps), so you may not need to calculate it - let SharePoint do it for you.
Hope this helps!