Cells, for example, are a central category, but there’s no definite criterion for what counts as a cell. If you attempt to find one, you rapidly bog down in a maze of exceptions. You might start with something like “a self-reproducing living unit carrying a single copy of the organism’s DNA within a membrane.” But red blood cells don’t self-reproduce and have no DNA. Mitochondria are not cells, but they self-reproduce using their own DNA within a membrane. Muscle cells have multiple nuclei, each with a separate complete copy of the DNA. Some algae have life stages in which they have no cell membranes. And so on indefinitely.8
I'm not an expert in biology or anything, but perhaps the moral there is we should rethink this 'cell' idea? IIRC astronomers continue to talk about 'planets' even though the longer you examine the concept the more incoherent it becomes. (For an extended example, see the infamous Discourse about whether "Pluto is a planet", which led to hilarious goal post stretching where people kept trying to find a definition of 'planet' that exactly fit the traditional celestial objects we classify as planets without having to include any new ones or exclude existing ones)
There is obviously no rule that says the categorizations we come up with for stuff when a field is young should be expected to have infinite inferential reach as that field of knowledge expands.