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No, AV has capabilities much more sophisticated then that, however from what I understand, within the malware analysis community specific samples are generally identified with their hash. In addition, if the hash of a file is known-bad, you can skip all the binary pattern matching and heuristics and stuff.

Most not-shit AV runs checks from easy to hard so it will blacklist/whitelist on easy identifiers (like hash) and only do a more in-depth look at greylist stuff

They used to do a lot of fancy things, back in the days, including running bits of suspicious executables in heavily sandboxed interpreters to spot behavioral patterns.

I'm guessing those kind of approaches have largely gone away, being replaced with signatures that are hopefully fuzzier than a wholesale cryptographic hash, but still essentially only catching things after the fact, which works well with subscription business models.

many modern ones have ML engines. Also some enterprise products can detonate the executable in specially created vms to observe what happens.