All the cutters I've seen mostly rely on the printer's physical movement to drive the cutting blade, rather than a servo. Technically there's the SnappingTurtle, by the same guy who made the BoxTurtle project, which appears to be closer to what you're looking for, but unfortunately isn't available yet.
That said, maybe take a look at the BoxTurtle project/ discord? Part of the project is the FilamATrix tool head, which is a mechanically activated cutter. There's also the AT4 tool head and the crossbow filament cutter (which you might be able to adapt to your old printer if you didn't want to do a full tool head conversion).