Hello @TimHoeflich1 - Thanks for sharing your feedback on this topic.
When we built ArcGIS StoryMaps we looked to provide more storytelling capabilities, a higher level of security, and make it easier to do many things that required special coding skills in the classic templates. There are now lots of things you can do with the builders that you needed code for in the past.
It would be great if you could provide more information about what you did in your classic story that required using HTML. Could you share some details?
At this time, using HTML code inside a story is not supported. This is something that may come in the future, but currently you can use one of the available themes or make your own custom theme selecting from over 1000 fonts, using your own colors, and choosing from different style options.
You can also use our classic conversion helper to assist the process of migrating your text and media to ArcGIS StoryMaps. Try the Classic Story Conversion Helper - Esri Community
We also have several helpful articles that provide tips and guidance for migrating.
The screenshot you've shared is a code block. The purpose of a code block is to include code snippets as part of your story. For example, you have a short Python script or Arcade express you want to share with your readers. Check out this story as an example of how the code block is used: Spike Maps (arcgis.com)
Owen Evans
Lead Product Engineer | StoryMaps