Help - no input at all with logitech m240 BT mouse (Saturn)

[bjfrench94]

Hi everyone
I've been toying for a few hours now with my new blueretro dongle (on updated saturn firmware 25.04, white japanese saturn)
The dongle works fine with two different gamepads (xbox series x and xbox one) in gamepad mode, haven't tried analog gamepadalt yet
But it doesn't at all when trying to set it as a saturn mouse (preset on "Default Mouse", output 1 on "Mouse") :
-> pairing is OK with my logitech m240 BT mouse (by the way, mouse itself seems ok and tested with other devices)
-> but i get no output at all (directions or buttons) when in game
-> when hot swapped on controller 1 plug with a compatible game (Worms, Yu No, also tried Policenauts), the cursor may get displayed (so i believe the console correctly identifies the dongle)

I get that this mouse is very low cost/low profile, even lacking a button to map "start" , even if I thought I could have gotten around that particular issue with manually mapping wheel up/down on start
Has anyone tried this kind of entry level mouse with success, or should I scrap it and buy a (rather expensive) m720 ?