Just chiming in because I noticed this as well. Some time ago in earlier 5.0 versions I was able to add a control rig to the character inside of Sequencer which only contained controls for setting curve values (morph targets in my case) for stuff like blinking and facial expressions. This was extremely useful because I was able to maintain the animation playing in Sequencer while blending in the control rig on top. Now it seems to override the sequencer animation entirely, so either I can use a control rig or play an animation but not both simultaneously.
It seems the only way to achieve an equivalent effect now is to select the “Edit with FK control rig” option which does allow me to keyframe in morph target values, but it also creates keys for every bone/morph value on every frame. Which is fine I guess, since I can bake the changes into an animation when I’m done anyway, but I preferred the previous method as it was a bit cleaner and quicker.