I couldn't find an off the shelf Flipper module, but the Lego Powered Up BLE protocol is fully documented by Lego:

https://lego.github.io/lego-ble-wireless-protocol-docs/

So it shouldn't be too hard to add one.

Keep in mind that as noted in this article, the default Powered Up Hub behavior is as a "passthrough pipe" to the host device, so just using a Flipper might be a bit obnoxious.

Older Lego trains use IR for control so if you just want to control motors and lights, you can get one of those and control it with the IR blaster on the Flipper. If you also want the sensors/newer programmable hub, then you need the BLE protocol.