Which will give me the most definitive results for hair transplant scar: PRP vs Minoxidil+Dutasteride vs Microneedling?

Neither medication nor PRP will promote hair growth in scar tissue, given that the scar does not contain follicles. If your FUT wound was closed with a trichophytic closure, hairs in the lower layer may poke through the scar tissue to conceal it, but generally speaking scar tissue does not contain follicles.
Your options for concealing your scar are:
1. Scalp micropigmentation. This is effective, but ultimately temporary and likely will need to be repeated every few years, assuming you go to a skilled artist.
2. FUE grafts directly into the scar. This will place follicles in the scar tissue which will then grow hair. See link for an example case.

Very hard for follicles to grow where there is scar tissue, keloids and scarring unfortunately is always a risk when doing FUT this more likely genetically to form things like keloids, hypertrophic scars in patients who have a darker skin tone. You can continue your prp minoxdil + prp and dutasteride to keep the new hair transplant follicles viable. . I don't even think micropigmentation will help..