Hello IIVQ,

The switch for the way https://www.openstreetmap.org/way/698922430 from highway=track to highway=footway is a little bit suspicious. This way is quite large. More over I have some doubt that this is an exclusive way for pedestrian (basic definition of the highway=footway).
Are the ways https://www.openstreetmap.org/way/1423942398 and https://www.openstreetmap.org/way/1234133593 more something like highway=path + bicycle=designated or at least bicycle=yes?

If you want to indicate a MTB route it will be probably better to add a MTB route relation more than putting all MTB tags on the way itself. The attributes piste:*=* are only for skiing. Take a look as example to the bike park in Serre-Chevalier (example https://www.openstreetmap.org/relation/9228387).

Best regards, 

Patchi