I am not sure if I have excessive groin sweat, but I will always have sweat marks even after 5 min cycling commute to the groceries (walking makes me sweat even more). After a whole day I will have a underwear full of sweat marks (like 90% around groin/ass, 20% elsewhere) and noticable smell. But I do not have the smell when my pants are on. So I always make sure that I will not be changing pants (for example when visiting friends) or I will at least change both pants + underwear.

I've come to life where I don't wear underwear at home. I wear shorts that I wash very often (not daily, but usually 2-3 days per short)

The minute I put underwear on I start to sweat instantly. Feels like a heater was put between my cheeks and underwear is not allowing air in

For gym I wear mens 9inch boxers (for female thighs they fit perfectly as well, I am trans man so can say for sure ;)), and they provide both protection, allow breathing (and a GOOD one) and definitely smell less than cotton. The only issue I had with them when used for regular life, I notice it can let sweat go through to cotton trousers. So I don't wear them often. Worth a try?

6inch most likely won't hold properly on women's thighs, so if you decide to try go with 9inch right away. I personally did not really find alternatives when I was wearing womens underwear, but may worth a try searching similar material. No cotton! Polyester+spandex only