As a father who is suffering from plantar fascitis (brought on by running), I would rather fix the problem by strengthening my arches than mask it by buying inner soles.
https://www.google.com/books/edition/Born_to_Run/4gS_0UwVI34...
I've had plantar fascitis a couple of times before (decade apart) and I've found that it can be resolved within 3 weeks.
The trick that worked for me is to regularly stretch the foot / arch after a few minutes into a walk when the foot is warmed up. If I do that consistently near the beginning of every walk, the pain quickly fades away and the problem resolves itself.
I think hiking over technical-ish terrain, like stumbling over tree roots and rocks that hit the arch would provide the same action of stretching of the bottom of the feet.
That said, proper insoles are the lowest-effort, cheapest means of mitigation.