I once heard someone say secret exits kinda suck. And i kinda agree. Seeing a Red rot makes me go 'ugh lets look for a key i guess'. Yeah i also used secret exits in all my hacks so far, but i don't know if the majority of people really wanna explore or just have some platforming Action.
Just like with any level design element, there are ways of making secret exits awesome, and there are ways of making them awful.
Imo, unless a level incentivizes this with replay value, offers a new route, or is explorative / open-ended in nature, I would lean away from adding a secret exit. Placing a key and keyhole somewhere in the middle of a level without introducing content other than the necessitating an exit clear and opening a different overworld path might not enhance the gameplay experience, instead, it can instead feel tedious for the player.
Something I'd like to do more of with secret exits is simply taking the opportunity to send the player in a completely different direction, perhaps to reflect what the overworld tells us. Creating an entirely new path for the secret exit gives it a realistic purpose.