Hi !!!
I think that
Briar is pretty unisex.
On a girl it reminds me the famous princess but on a boy it is linked with a rose garden in my mind.
Infact in Italian 'rose garden' is
roseto that would be a wonderful masculine name if it were actually used (unfortunately isn't).
So
Briar has the same vibe of Roseto in my mind plus it is enough similar to
Brian and
Blair to be perfectly masculine.
I personally prefer
Briar as masculine and something like
Eglantine for a girl.
Personal Name Lists
https://www.behindthename.com/pnl/125456