I agree with ATCguy; If it ain't broke, don't fix it.
In my experience Flex-Seal will hold up OK. It's the Sun that will do it in over time. If you really want to remove it first heat it up with the low heat on a heat gun than use a plastic putty tool to work it loose from the edges toward the center. Go slow to protect the membrane. Again, if there are no leaks I'd leave it alone.
Open Road Pathfinder
2020 Kodiak Ulta Lite 201QB
2018 Ford F150 Twin Turbo V6
Logging the miles in the USA. Adventure awaits around every corner.