Possibly pliable and moves with the actuator in order to maintain stealth in deflected positions. Otherwise, deflection may reveal some non-stealthy surfaces (whether by shape or inability to use stealth covering in between moving parts with tight clearance).
Yes, they are flapperon/elevon actuator "gap seals", there are also similar "flap gap seals" between the trailing edge of the main wing and leading edge of the flapperons/elevons.
Note there is a stiff fairing over the leading and trailing edges of the actuators, likely carbon fiber, and this flexible gap seal closes bridges that gap when control surfaces are deflected out of the in trail position. They are fixed to the front section of the stiff leading edge fairing, allowing the trailing edge stiff fairing to push them aside as needed for clearance to actuate the control surfaces.
they serve a primarily aerodynamic purpose, streamlining the flap actuator assembly, and preventing the leakage of high pressure air from below the wing between the trailing edge of the wing, and leading edge of the flapperons/elevons.
I believe we can see that those gaps on the trailing edge of this flexible seal close up as speed increases, and control deflections are minimized by the FCS.
Now they also do reduce RCS spikes due to hardware that would otherwise be "hanging out in the breeze.