Let's be clear. There is no real substitute for coffee. The best we can hope for is something reasonably similar to adjust to if needed.
Fortunately, chicory root comes close. I rather like it. I've grown it. I've been roasting it myself for 15 years or so and usually have some around. I hadn't had a cup in a few years, but the other day when I found we still had plenty in stock from my husband's garden it got me thinking about it. Since then I've raided the cupboard a few times until I found I was low on it.
This morning I roasted another batch.
Below is what it looks like as ground, dried chicory root. It is a very moist root. I've discovered over the years it is best to dehydrate it and then roast it.
If you've more patience than me, you can skip the dehydration step, but you'll have to watch the roasting very closely.
Here's the midway point. I did it at 350 degrees for about 40 minutes. I stirred it every 10 minutes. I cannot recommend using a higher temperature. The root is very finicky. I did it at 375 once. The stuff around the edges gave me a very dark roast.
The above is medium roast.