the active record pattern, as it is commonly used, does not set you up well to lift individual components out of a monolith.
That said, for microservice extraction specifically, a bit of creative metaprogramming/monkey patching of AR to identify & categorize your callers is probably easier.
the problem with activerecord is most people usually don't put this in place to begin with because the active record pattern makes it easy not to, which creates a massive pile of spaghetti code long term.