How to quickly add Landsat and set your own custom functions.
In Pro - Go To Project, Click on Portal (I'm assuming you are connected to ArcGIS Online), Type Landsat in Search, Drag and drop the service on the map. Click DataTab, then Processing Template. You will see a list of all standard templates with a range of band options. Check these out, they may be what you want.
You can also set to None, which will return an 8band service. Suggest you make you screen smaller temporarily (as there will be more data being transmitted). Now create a raster function to create any set of processing for the different bands etc. Test them out (processing done on Pro) and then save as new as a Function chain say to your custom category. Go back to your Landsat 8 Views layer, click again on Processing templates. Go to the end and click on 'Add Custom'. Navigate to the function you saved (you may need to press F5 (refresh)) to see. Add the function. Now the function will available in your Processing Templates list. The function will be sent to the server and executed there. Only the results will be transmitted back to Pro (much less data then 8bands 16bit). Expand your screen again. Don't forget you can also in the Data Tab change the compression used to transmit the data from the server to Pro.
