Custom Symbology not an option anymore?

[KamillePreto]

I have a Web Map with our Asset Management data.

I created symbols in Illustrator for our Inlet & Manhole datasets, which I had uploaded on here at some point - maybe about 6 months ago. I set the style options so that the symbol would get smaller as you zoom in, as you can see on the legend. I honestly just applied random numbers to it until it worked appropriately.

My issue is now, on the Dashboard I created... the legend pops up exactly how it shows on the screen (with the numeric values that mean nothing for our data). So I was going to re-do the symbology as the "Location (single symbol)" option with the custom symbology. But there is no way to upload the symbol anymore.

Is this gone from the new map viewer?

How can I work around this?