I think most classes are inherently “multi-level”; think about it, within a group of beginners, there is a range of experience, right? Of course this pattern goes up the chain to the self-described advanced exerciser.
My most common strategy is to have a focus for the class and communicate it to the participants at the outset, i.e., anaerobic training, heavy weight lifting, improving balance, etc. This way, they already have some idea of the demands that will be placed on them (with these I always offer safety cues and reminders to please “work at a level that’s appropriate for you”. I like to say that there’s a sweet spot between comfort and challenge that clients must find).
I always begin with a base move that everybody can do and that done mindfully and properly provides a good workout, as is. Of course, I’ll add progression and regression options throughout so people can literally exercise their autonomy and work at a level on which they feel confidently challenged.
I like to mingle in the group during the class; do the exercise beside them, maybe offer a helpful cue for improvement or words of encouragement or praise, when appropriate.