Ender 3 S1 board2.2.4 STM32F1 Firmware?
I'm currently running the "Pro" firmware on this machine and it's having a difficult time connecting to Repetier. Is there a Repetier firmware I can flash the machine with that will make it more cooperative?
I don't know the board so it is not officially supported. Dev 2 might be able to tweak it with new definition and pins, but needs a developer with board to do that. So short answer is no.
What firmware is "Pro"? Marlin or own firmware from ender?
What is your connection problem? In case of problems connecting it is often helpful to enable ping-pong mode. This makes sure only one command at a time is being send. Sometimes parallel communication (which is faster) does not work reliably.