When do signs of fear reactivity typically show in puppies?

Just a question out of curiosity. My pup is currently 6mo and fine with other dogs. We’re working on neutrality as he’s a little excited (just friendly but still a bit bouncy haha), using techniques inspired by BAT 2.0, but just curious as to when signs of fear reactivity start to show so I can be aware if they do start to appear.

My last dog was reactive. I got him as a teenager and never properly trained him, which I’m very regretful of. He had a fantastic life, and 100% recall all the time, but was somewhat reactive to other dogs and in retrospect I wish I’d fixed it. So I’m keen to prevent/avoid it in this new pup.