Overwatered yellow is bit different. Leaves get plump, visibly water-logged and watery yellow. If drying from underwatering, it is more drying of the leaves (first they may start getting wrinkly/shrivelling).

In the photo above, the bottommost leaves are yellow and plump but the second layer from the bottom are shriveled. Therefore the conflicting signals!

This looks like Graptopetalum mendozae. In more light it will take on a nice whitish/silver colour and yes, its quite etolitated. These guys prefer a lot more light.

Is there soil under that grittyish mix? What kind pls?

Hard to make ID on such stretched out plants.

Yes its pumice, potting soil and gravel. I think Whitters got it right with Graptopetalum Mendozae!