Does wearing a braces weaken muscles? have spasticity, and was thinking about wearing one to see if it helps?

That depends. The bodies mobility and function is often aided by the interaction of various slight stabilizing movements in muscle groups. A brace worn constantly can take some of the stabilizing efforts out of the equation and those muscles can weaken. Using a brace that may improve your mobility is a good thing, but taking it off occasionally can preserve the other function. Talk with your PT

In the presence of spasticity which can compromise ambulation, the use of appropriate customized bracing systems may be stabilizing. But this must be used strategically and intermittently to prevent muscular atrophy and weakness. See a physiatrist and get assistance in designing an effective approach.