In Silicon Valley. At least two neighbors had pool tables in their open covered patios. Sliding door from the house to an open covered patio.

They had no problems. I do not remember players commenting on the playing surface.

Your situation may depend on your local weather and the pool table used.

Please try to consult with your local pool table dealer.

The surface is stone, should not be affected by humidity, but maybe the wood or felt.

Felt will grow mold in high humidity, wood may move, wet to dry. Ball baskets will mold in high humidity.

Thanks Matt, totally appreciate your feedback. . We are in KS. We are putting in radiant heaters, so even if cold out it will be pretty cozy. Our summers are hot and humid, but not usually extreme. This will be LL walk out, through big double door slider onto screened in covered patio. I will more than likely put down an outdoor rug to cover the majority of space. I think it could be a lot of fun, as we will entertain on that LL, since that is where or bar also is. lol