I looked it up but could find a helpful answer to this exact problem.

1) I am trying to mirror 2 things, one is a cut-thickness feature but it is not letting me and I don't know how else to mirror it to the other side of the glasses.It says the surface could not be thicken

2) I am trying to mirror the nose pad i did on one side it is not working, i have tried to mirror the actual sketch and doing everything double, mirroring features, mirroring body, everything but cant make it work.