Hopkins did appear in the pre-Broadway Roundabout* revival of Old Times with Marsha Mason and Jane Alexander in the mid-80s. He also opened M. Butterfly on the West End in 1989, but that does appear to be it regarding his theatrical ventures.
I thought Peter Gallagher and the supporting cast were all good in that revival of The Country Girl, but McDormand and particularly Freeman just didn’t gel.
*The Roundabout produced off-Broadway productions during the 70s and 80s. Their Old Times did not later move to Broadway.