Route plotting"

There are three options;
"Most Popular
Routes others use most",

"Most Direct
"Minimise distance"

"Freehand
"Draw your own route".             

Previously, there were the following options:

"Most Popular"
Routes most used by others,

"Follow the roads"

"Freehand drawing"
"Draw your own route". 

With the "Most Popular" option, there is no problem if "follow roads" works, even if they haven't been used before.

I found that it follows roads in both options (Most Popular and Most Direct). However, it uses a different method for each. When the "Most Direct" option is selected, shorter "dirt roads" become available for "road cycling".

The dirt roads are probably not that popular for road cycling. You can try making it use those roads by putting the points closer or right on the road.

I actually don't want to do this, but that's how the program works. Actually, the program needs to use paved roads for "road bike".

Nahh, lots of dirt roads works great with a road bike. As long as they are hard enough and without gravel. I'm stuck on 25 mm tires since my fork can't take any wider. Otherwise I would go to 28 or 30 mm. Where I ride there are lots of hard dirt roads between nice paved roads so I use them to find the best course for the day.

Here is where Strava routing is a lot better. You can see what type of road it is routing you on so you can make it chose a different road if you just want fast paved roads or if you can accept some unknown roads or shorter dirt roads.
The popularity of each road is also displayed in a great way so you can find roads that will work for a road bike but the routing isn't using it. Garmin's heatmap is not good and easy to see and if you zoom in it disappears. 

Actually, that's not a problem for me because I have a Gravel bike, and I mostly use that. I generally use mixed routes. I just wanted to explain how the program works.