You should be able to select just the portions you want. Did you try the adjustments described in the online manual?
Get the Details You Want (Keyboard Shortcuts)
To pick up light markings, use Control-Up Arrow (Windows) or Command-Up Arrow (Mac). To ignore light markings, use Control-Down Arrow (Windows) or Command-Down Arrow (Mac).
If there are too many stray marks, Control-Shift-Up Arrow (Windows) or Command-Shift-Up Arrow (Mac) to remove them. If small details aren’t showing up, use Control-Shift-Down Arrow (Windows) or Command-Shift-Down Arrow (Mac) to reveal them.
If you still can’t get a clean scan (too much “noise” in the original, for example), you might consider using a free app like Adobe Capture to import scans from a phone or tablet into Inkscape / Illustrator / Affinity Design for complete control.