When clicking on the icon:

2331.096 Error MainLoop.cpp:1183: Exception at tick 7185172: The mod Module Inserter caused a non-recoverable error.
Please report this error to the mod author.

Error while running event ModuleInserter::on_gui_click (ID 1)
ModuleInserter/gui.lua:278: Invalid element config_frame
stack traceback:
[C]: in function 'error'
ModuleInserter/gui.lua:278: in function <ModuleInserter/gui.lua:264>

To add insult to injury, when downgrading from 4.1.2 to 4.1.0, the mod crashes in in on_upgrade and saves cannot be loaded :*)

Can you upload the save somewhere? Just clicking the button doesn't crash for me.
Did you add ModuleInserter to a save or upgrade from an older version?

The latest update won't crash anymore. Let me know if you still have issues.

Are you by chance using https://mods.factorio.com/mod/TrainsSignalSender ?
This mod deletes all other gui elements when creating its own, which would explain the error.