No, there is no believer. But sometimes it feels like there is because thoughts saying it's that way repeat and loop.You wrote "but still frequently fall into believing the thoughts in everyday life."
What is it exactly that sometimes fall into believing thoughts?
Is there a believer separate from the thoughts believed?
Reflecting on this brought up something for me, around the yo-yoing of clear seeing and not. So, when clear seeing is happening I can categorically say that there is no self, everything is just happening and so on - there is absolutely no room for doubt. And when you asked 'Have you seen without doubt that there is no self/I with any substance or as entity with any sort of power?' then the answer is definitely yes - I have seen this.
Then there are times when clear seeing isn't happening and I'm not sure - there are repeating thoughts about 'unsureness'. Since there is no self, and no past and future in the present moment, then when I'm 'wobbling' there isn't some underlying 'me' that knows there is no self. At that time 'I' am not seeing in the present that there is no self. I guess what I'm saying is the yo-yo-ing effect means that the answer to the question varies depending on when you ask it, because there is no permanent thing or state.