I was too verbose in the previous post. Let me summarize:

The all_users_control_menu doesn't make all plugged controllers control the menu. Actually it just makes all controllers bound to a player control the menu.

If I have a plugged controller not bound to any player, this controller can not control the menu.

Changing Device Index on-the-fly still can bring some unpleasant situations, like I detailed here (the all_users_control_menu decreases the chance to make it happen, though).

Coincidentally I have purchased and tested a cheap USB hub with 7 ports on my raspi1 today. Some ports doesn't work as expected, but I didn't have time to check it deeper.

Did you turn on the "Save config on exit" in RetroArch (config_save_on_exit = "true" in retroarch.cfg). I'm not sure but by your description it seems to be your problem (at least one of them).

BTW, maybe you like to know this tool: https://retropie.org.uk/forum/topic/1167/here-is-a-way-to-select-joystick-for-players-1-4-global-or-emu-specific

please~~
My host is Piboy DMG,
I want to connect two external joysticks, Play1 + Play2,
But I want Piboy DMG built-in joystick and external Play1 joystick to control Play1 together,The Play2 is another Play2 joystick, the joystick is PS1 specification.

1659585356430-s__29237252-1_1_1.jpg

1659597545896-2022-08-04_151404.png

Because when I set up the two joysticks, I also set the "Combo" button, the Play1/2 joysticks can be sure to combo, but the built-in joystick of Piboy DMG can be controlled but cannot be combo.

Ths.^^