20+ year software engineering professional here. I’ve seen this topic posted multiple times and in all cases users are told the active tab is different (i.e. it’s good enough, why are you complaining?). I’m telling you plainly, it’s not.
Are the text colors different between active and non-active tabs? Yes.
Are they different enough to be distinguishable and provide a good user experience? Absolutely not.
The only way I’ve found to actually tell what tab is active is to look for the close icon, but that’s still a hunt to find.
Dark Mode GTK theme - barely different
Dark Mode Classic theme - active tab is a slightly lighter dark grey pill
Light mode active tab - clearly different
Adding a config option to set the active tab color for the current theme or as a global override should be trivial. You already know how to target the current tab. Are there docs on making a custom theme? If there are, they’re not in the Appearance settings pane where they should be.
Is this a big, functional change on the critical path? No.
Is it a change that many, many users are asking for, over and over again, and being ignored? Absolutely.
Try listening to your users and plan the tech debt in an upcoming sprint. You’ll spend less time fixing this than you will addressing comments on yet another thread like this.