can anyone give your opinion on the below terms based on your understanding? In what conditions the deposit is not refundable?

“Refundable if we are appointed as the main contractor for all construction scopes only and will be refunded only after the renovation deposit is received”

Yes, that is my understanding as well, but it is not.
The phrase is stated in the design fee quotation.
Deposit has been paid before design/3D drawing.
After 3D drawing, I appointed him as main contractor.
At the final stage of reno, he said the deposit is not refundable. He said “The refund of the design fee will only be eligible if we were appointed as main contractor for all scopes from A-Z including furniture purchase, curtain, bed frame etc. Only sofa and bed I use back my existing one, fan I purchased, curtain I engage curtain maker before the project and already inform him during the 1st meeting, and he accepted but verbal only.
So I am wondering is this common in the Interior Design and Build world.

This is a painful lesson learnt. Construction to my understanding should only cover the activity of constructing every single piece of an object on his own, not purchasing a ready made object.