After finishing the course of creation character from Grant Abbit, I decided to do an experimental - combining Rigify and motion capture (mixamo) into one rig so that I could conveniently switch between one rig and another.
As the model from the course and the whole animations are tested, I did not waste time on additional weight adjustments, so there are visible mesh deformation errors.
The most important thing is that the whole thing works well, I have Rigify in one rig (with all functionalities, as well as the ability to attach Mixamo animations
Soon I will do a tutorial that explains how to combine both rigs.