Ignore post - Search is not delegable with SharePoint lists. I was not getting the warning on some of my formulas because the Search was on the outside of another Filter.
The behaviour of PowerApps marking what is non-delegable is a bit confusing in these circumstances.
I have an app using SharePoint lists as the datasources.
Each list has a 'View' screen with a gallery where the Items property is a Search of the SharePoint list, with two or three columns included.
In some of my lists/screens, the Title column from SharePoint is non-delegable (while all other text columns are fine) but in other lists the Title column in the Search is delegable.
I have tried adding an index in SharePoint for the Title columns that are coming up as non-delegable but that didn't make a difference.
Below is the text for my gallery source. Only the Title column is marked as non-delegable (blue underline). Similar searches on other lists including a Title column do not have any delegation warnings.
Any suggestions as to the cause of this inconsistency?