Well there are numerous definitions around for agnostic and atheist, some atheists object to the definition “the absence of a belief” in fact, spare a thought for them!
Whether one holds a belief or not is a consequence of the assumptions that one chooses to make, at least for the rationalist.
Saying “I’m an atheist” is equivalent to saying “I have made certain assumptions about reality”. But it leads to problems. For example an atheist might say “I’ve never seen evidence for a God” yet how can they know that is true?
How can an atheist distinguish between something that is evidence for God and something that is not? They can’t, I’ve asked plenty of them over the years. If they cannot clearly explain how they would distinguish these two then their position is somewhat vacuous.