A 10 speed chain will not mesh well with an 11 speed cassette. It’s best to use the same cassette (number of speeds as well as the gear range) that’s on your bike for this exact reason.
Assuming you’re using a wheel-off Wahoo trainer: the large flywheel will continue to roll - that’s what gives you the smooth rolling feature. It’s best not to apply the rear brake - especially if your bike has hydraulic disc brakes. Applying the brakes without the brake rotor in place will close the gap between brake pads. Next time you try to put the wheel back in - the rotor may not fit.