PPete2
The method to "classify hiking trails in mountainous areas with regard to the difficulties to be expected. " within OSM is the key "sac_scale".
This path is correctly tagged with "sac_scale=demanding_mountain_hiking". What this mean you can read at https://wiki.openstreetmap.org/wiki/Key:sac_scale

Of course you have to use Apps and maps which are displaying the different sac-scales of paths. An example is OpenAndroMaps.

The standard map at openstretmap.org is NOT an appropriate hiking map.