Conditional Formatting Task Tracking

I have been using Project for decades but I do not know the terms "tracking line" or "back spike" specifically with regard to your question. If you can manually mock up an example of what you want a past-due task to look like I'm sure the formatting part will be straightforward. Also, all of your tasks in this example are in the future so none can be past the due date (well, some are in 2018 but your timeline doesn't back before the 4/10/2024 project start date).

Are you talking about the red lines, the red dots, or the black line in the middle of the task bar? My version of Project (2019) doesn't show the red dots/lines so I'm not clear on how to read those symbols given the data you are showing. The black progress bars are probably for % complete.

You can't add a bar in the middle of a cell, a dot in the middle of a cell, or red lines between cells in Excel cells using formatting. What would be ideal is showing in the Excel file what you want it to look like for those late tasks. For example, you could make cells red instead of blue to show what a late task's progress should be.

The bottom line is that you might be able to put some kind of indicators in Excel to show late tasks but you'll never get it to look just like Project.

So I have a dumb question. If you have Project, why are you using Excel for this?