How is the recommended route for cyclist planned?

I am struggling a bit trying to find some documentation in regards to what parameters the “recommended” routes for cyclists are based on. Is it just a balance between having the shortest and fastest route or does it also take in factors like bicycle path vs. being on the road, avoiding roads with high speed or lots of traffic?

for the cycling profiles, the recommended route preference also takes into account how well a route is suited for biking. This is done by giving each street a priority. The priority is calculated from the tags, such as cycle path or if it has high speed limits. The process is quite complicated.
This priority is then used in combination with the “fastest” option to give you a recommended route.