Will Scar from Subcutaneous Forehead Scar Be Noticeable?

Every browlift has its plus and minus. There are now "hybrid" procedures which do not involve the typical jagged anterior hairline incisions, and actually remove a section of widow's peak. The scars are almost universally excellent.
As in all plastic surgery, there is a huge artistic component beyond the "what procedure do you do"; it is as important as the procedure being chosen who is doing it.
Endoscopic browlifts are fraught with several problems. First and most concerning, they move up the hairline. In fact any browlift originating from above the hairline moves up the hairline. That translates to a high forehead, which can give a prematurely elderly appearance. In many patients it is not an issue, but in many, particularly those above 40 who are noticing their hairlines receding, it is an issue. Also endoscopic incisions typicallly cause some hair loss around the incisions, resulting in 3 small bald spots above the hairline.
Coronal incisions (ear to ear) are still used, but also move up the hairline considerably and often result in numbness due to division of the supraorbital nerve deep branch, which is spared in most other forehead lifts.
Experienced surgeons are familiar with many techniques, and use them to benefit their patients maximally. You may wish to read our book chapter on forehead lifts in the textbook Mathes, referenced below.

It might be visible but often not. There are some great means to make it less visible including beveling the incision so that hair follicles remain behind immediately below the scar and will often grow through it. Also other camouflage techniques include micro hair grafting of even using tattoo stippling dots that will mimic hair follicles.

Whenever there is an incision, there will be a scar.  Scars are unpredictable and healing has many variables.  Having said all of that plastic surgeons usually place scars in areas that are less noticeable.  The incision for this operation is usually well tolerated.  Please talk at length with your surgeon about your concerns.