The latest version 5.1 firmware update for Leica’s SL2 and SL2-S cameras is designed primarily to improve flash photography with Profoto units. However, as always, updating the firmware is recommended in any case, especially since this latest version also aligns firmware between the SL2 and SL2-S.
It is interesting that it does not mention the new non-APO 35mm and 50mm lenses. Would the new firmware not be needed for those lenses? In the past I believe Leica has always updated the firmware whenever a new lens was released.
Luckily, they do not release many lenses to keep firmware updates minimized