Can powdered probiotic supplements make thrush worse?

Yes!, they can. Not All Probiotics are created equal!

by definition probiotics are a form of "yeast"

Thrush is caused by a specific type of yeast. Candida.

A Candida over growth is the cause of Thrush.

There are over 2,000 different species of "probiotic" and yes some of these can be " commensal" or a type of that would live with and help Candida.