For those that have played the main quest, when would you say is the best time to stop and explore? No spoilers, if possible, please.

I'm still relatively early in the game. Haven't built up the camp. I want to continue doing side quests and exploring. However, many games like this have a point in the main quest where stuff is unlocked and it makes sense to go off exploring. Really I just want to know if there is much locked behind the main quest. I've mostly stuck to Hernand and am enjoying myself. Just curious what others have to say in this regard. I dont like the idea of doing a ton of side content only to find I missed out on a bunch of abilities or unlocks that would've made the game more fun. Then again the game feels like a slow burn and I've been treating it that way. I'm indecisive apparently.