Last season Grandal got 215 AB's in 72 games with the Pirates. Think he got some time on the IL, but even when he got back, with the emergence of Joey Bart, he was still kind of in a part-time role.
I think he would sign somewhere to catch 30-40% of the time, and get his 250-300 or so AB's. Like some others have said, he likely doesn't sign anywhere as a starter, unless a team loses their No. 1 catcher to injury.
As for Kirk, can he catch 130-140 games per season? I think it's a good idea to have a reliable partner with him in order to keep him fresh. Having Kirk start 110-120 games behind the plate seems more reasonable. Plus, bringing in Grandal allows you to use Kirk at DH, let's say if his bat reverts back to his 2022 form.