I want the indicator to reflect the current state - whether the tab is in reading view, in source mode, or in live preview (a new icon or simply no indicator), and I don’t need it to be clickable. I’m using Minimal theme, if that matters. And I like having “Show tab title bar” disabled.
How deep did you look into the CSS option? I used CSS to move the Sync icon out of the sidebar on mobile — thanks to the wizards in the Obsidian Discord’s #appearance channel — so it might be doable with some magic.
I’m not a wizard but I think I know CSS and HTML well enough to understand that you can’t posibly “style” a single icon in the corner into an icon on every tab that would show the current state the tab is in.