Offhander

A small mod that adds a Keybind for dedicated Offhand use (by default Mouse 4) and a bindable Keybind for dedicated Mainhand use.
By default MCs handling for the Use(right-click) keybind is:
– check for block interaction (buttons and co)
– check for Mainhand interaction (check selected slot for interaction)
– check for Offhand interaction
    
if an interaction is found the others are not checked. This Mods adds 2 more Keybinds into the game, allowing for eclusive
– check for Mainhand interaction (check selected slot for interaction)
    
and an exclusive
– check for Offhand interaction

this allows you for example to block while holding a trident or to not place offhand torches while building when using the dedicated keybinds

Im unsure if anticheats might not be happy about players beeing able to block while holding a bow/trident or similar. Use at own risk.
It does NOT allow you to execute two interactions at the same time! It just allows you to have more control over which interaction to use.