I think you might be thinking about this too literally. there is no such intrinsic property as either “stock” or “flow” - it’s primarily about how to interpret financial statements and, importantly, noticing that the balance sheet and the income statement have different dimensions, and that these dimensions reflect different causal states.
also, to be clear, this has next to nothing to do with the asinine “stock to flow” concept. this is a framework from dynamical systems applied to finance as a helpful heuristic.