Error is: prototype binoculars must be stack_size 1, when stackable is false.

Thanks for the report.

However, I am not quite sure what I can do, because this is already the case:

{
    type = "capsule",
    name = "ZoomingReinvented_binoculars",
    subgroup = "tool",
    order = "z[binoculars]",
    icons = {
        {
            icon = "__ZoomingReinvented__/graphics/binoculars.png",
            icon_size = 32,
        }
    },
    capsule_action =
    {
        type = "artillery-remote",
        flare = "zoom-in-flare"
    },
    flags = {},
    stack_size = 1,
    stackable = false
}

https://github.com/Jarcionek/Factorio-Zooming-Reinvented/blob/master/src/data.lua

Given that it works with base game and a few other mods that I use, I am afraid that the problem might be with something specific to Big Bags and I have raised it there: https://mods.factorio.com/mod/BigBags/discussion/5cc73c08c65347000cda5b30

Maybe BigBags is unable to uninclude it, when the type is capsule.
I have other mods, that use the type "shortcut" to get the item in the toolbelt on the right . (where the copy and paste buttons are)
Maybe a solution for this? It also fits for what this extra bar is used for now.

Converting binoculars to a shortcut and adding a flag that in can only exist in the cursor is on my TODO list, but recently I didn't have much time/interest in working on that. If you would like to contribute, feel free to open a Pull Request in my Git repository ;)