Even a super-breathable jacket may need a bit of help keeping you sweat-free if you really start putting the effort in. Many jackets at different price points will overcome this issue by including vents.
At the lower end of the price scale, vents are used as the main way of allowing water vapour from your sweat to escape, so you tend to see large vents located on the upper bag, which is one of the sweatiest regions.
On most jackets that feature vents, they’ll also be located under the underarms, for obvious reasons.
As you go up in price, the vents are there to complement the breathability of the fabric, and can really help avoid that boil-in-the-bag feeling. These will tend to be on the underarms, with a zip closure so you can open them up when you need.
There’s an obvious trade off here as having open vents allows rain to get in as well as sweat to evaporate out, so they’ll tend to be located where they’re slightly sheltered.