I have just found out, how to enable rumble in pcsx2 for batocera 5.23:
When you enable rumble from the pcsx2-config gui you also have to set the Rumble intensity (just move the slider more to the middle. In the middle the intensity is the biggest. When the slider is on the maximum far left or maximum far right, there is no rumble).
After that, start the game via "System", "Boot ISO (fast)". But you have to run the game you want to play at least once before you do this. So at first, start the game you want to play normally, then exit the game and in ES Main Menu press F1, go to applications, pcsx2-config and change the settings and then within pcsx2-config go to System, Boot ISO (fast).
Unfortunately the setting-changes will always be lost, after you restart/exit PS2 games 🙁
This is a known issue and i hope one of the devs will work on this and fix it for a future release.
@nadenislamarre you have this issue on your to-do list?