Polycotton is great for dry and semi dry to mildly humid conditions. I don’t find it as comfortable in sopping wet, really humid conditions though (unless you’re more specifically talking Dri-Release type stuff which never uses more than 15% cotton).
When i was in Costa Rica, while more active (like hiking up a volcano) i wore a white OR Echo ls shirt in sun or a NB part nylon, part poly, thin, very breathable sleeveless t when in shade. When just leisurely walking around (still sweating my arse off though), i wore an all linen shirt.
Occasionally, it can feel like the above in VA where i live and similar clothing principles apply. I also like thin, knit, all or mostly nylon wicking shirts for the above conditions too. I’m not talking about the woven, button up type shirts, but much, much more breathable ones like the Duluth Trading (“underwear”) shirts.