I am going to share a useful video I have used to help with this process. Also, there is some additional information that is needed to be known. AGOL doesn't love raster's projected outside of Web Mercator in a Web Mercator projected map. If you want to use a different projection, the basemap must be your raster and your raster only, you even have to remove the Hybrid Reference Layer. To make things easier, I always collect my raster's in Web Mercator so I can overlay Esri basemaps with mine.
There are two ways I use to share raster's to AGOL
Gov pays homeowners to switch to solar (youtube.com) - this YouTube video walks you through the steps on how to generate your own tiles manually and share online, so you are not consuming AGOL credits (I recommend writing these steps down, so you don't have to rely on video). One time this took me 15 hours because I was generating over a million tiles and my computer wasn't outfitted for this. THINK ABOUT YOUR PROJECTION.
The other way- after you clean up your raster(s) and if you are using ArcGIS Pro, highlight all your layers of interest and then right click to and go down to share layer to online, go through the motions of sharing. This way will generate tiles and consume AGOL credits. This works much faster.
I will also share my word document I use, for when I manually generate my own tiles. There are some additional notes that will help speed things along and there is a model builder that helps me project my unprojected raster's by the masses (120+ raster's at a time). IGNORE MODEL BUILDER unless you think you need it.