That's an interesting observation which is new to me.This image for example clearly shows daylight shining through the gaps between the exhaust nozzles. It would be somewhat strange to have gaps if the plane had YF-23 style fixed exhaust troughs. But then again, what do I know?
I mean if not for TVC why would there be random gaps between the nozzles? So that argument makes a lot of sense to me.
At first glance and at low res, the nozzles look seamless with the hull and therefore rigid. But that might actually just because they have the typical insane build quality as everything else PLA, where the surface look seamless even if it consists of movable parts.
I defer that there is possibility of TVC, although it's nowhere as obvious as on the J-XS