The question is asked many times, rules differ from resort to resort.
Generally men are required to wear long pants for evening meals along with a collared shirt (golf shirts are fine) and no open toes shoes (Sandals or flip flops).
No sleeveless muscle shirts as well.
It only takes a few minutes to get ready for your evening meal, we all need to have the normal triple S after a long hot day in the sun on the beach or by the pool. So dress up in some with light slacks and a nice light shirt and enjoy the evening as you would in a restaurant in the summer at home.
Don’t take the chance that you will not be admitted to an a la carte or buffet for improper dress.