REROUTING - turn by turn

Hi everyone,
I haven't been able to resolve this problem for over a year now.
I don't even know if the problem can be solved in the settings of my fenix 7 or via software (Garmin Basecamp – Garmin Explorer
– Garmin Connect) or third-party software.
Here's the question = When I go on excursions (mountaineering) I need the watch to show me the route to follow "turn by turn".
That is, having arrived at the car park at point "A" I would like the watch to take me to point "B" (= refuge, summit, ridge etc)
passing through the path "X" then "Y" and then "Z".
Up to here everything is ok.

BUT if for some reason (e.g. path "Y" is closed, impassable) I decide to change route on the spot, I would like the watch to
recalculate a new route for me to still reach finish line "B". INSTEAD the clock recalculates a new, totally absurd route for me
to return to path "Y" and not to finish line "B"

I'll try to clarify: if I don't follow the sequence "DEPARTURE from point A>(x+y+z)> ARRIVAL at point B" but I change route
and follow A>(x+k)>B, the watch suggests a absurd route to return to path "Y" and he doesn't understand that I have to get
to point "B" instead (once some time ago, instead of recalculating a route of a few kilometers that separated me from finish line "B",
he suggested that I go around the entire mountain, creating a new route of 40 -50 kilometers to return to path "Y"... . absurd!)
You understand that in this way the watch becomes completely unusable as a "turn by turn" guide

I don't want a straight line between point "A" and point "B" but I would like the watch or basecamp or explorer or any other software
to calculate a new route for me to reach point B
Can you tell me exactly how to set up the fenix 7 or the Garmin Basecamp or Garmin Explorer software or other software
to obtain correct turn by turn guidance?
Thank you