planned for this fall release.
Right now you can publish a web style and use those point, line and polygon symbols
No, unfortunately. Arcade's ability to adjust symbology is already pretty limited, and it certainly has no capability to make web requests to an image file elsewhere.
If you know what your symbols are going to be, why not just add the custom symbols to your map?
Does the new Map Viewer offer the ability to import custom symbols from a PNG like the classic version?
planned for this fall release.
Great news! I'm looking forward to this update.
Right now you can publish a web style and use those point, line and polygon symbols