Error while running event Todo-List-Continued::on_gui_click (ID 1)
Todo-List-Continued/todo/features/export_task.lua:6: attempt to index global 'global' (a nil value)
stack traceback:
Todo-List-Continued/todo/features/export_task.lua:6: in function 'update_export_dialog_button_state'
Todo-List-Continued/todo/ui/main_frame.lua:57: in function 'create_maximized_frame'
Todo-List-Continued/todo/features/main_ui.lua:69: in function 'maximize_main_frame'
Todo-List-Continued/todo/features/main_ui.lua:58: in function 'on_maximize_button_click'
Todo-List-Continued/todo/todo.lua:94: in function 'on_gui_click'
Todo-List-Continued/control.lua:20: in function <Todo-List-Continued/control.lua:19>

Got the exact same error. I tried to reproduce: Created a task with 3 subtasks - handling without any problems.
Saved the game, exited Factorio and reloaded. The error now occurs when opening the todo list (using the button at the top left.)

Sigleplayer, slightly modded. ( About 30 mods).

I have no experience in modding or bug reporting, but I am available to answer questions.

if i remember correctly, global table does not exist anymore, they changed it to storage. it looks like that's one of the error

I have next error when joint to my friend locally. i Just open to do list.
Screenshot:
https://drive.google.com/file/d/1_gm6aRjuxOAg_4yCaybG2bdEecXz8ipG/view?usp=drive_link

Le mod ✔ Todo List - Continued (20.0.2) a engendré une erreur non récupérable.
Merci d'informer l'auteur de cette erreur.

Error while running event Todo-List-Continued::onguiclick (ID 1)
Todo-List-Continued/todo/features/exporttask.lua:6: attempt to index global 'global' (a nil value)
stack traceback:
Todo-List-Continued/todo/features/exporttask.lua:6: in function 'updateexportdialogbuttonstate'
Todo-List-Continued/todo/ui/mainframe.lua:57: in function 'createmaximized_frame'
__Todo-List-Continued/todo/features/main_ui.lua:69: in function 'maximize_main_frame'
__Todo-List-Continued/todo/features/main_ui.lua:58: in function 'on_maximize_button_click'
__Todo-List-Continued/todo/todo.lua:94: in function 'on_gui_click'
__Todo-List-Continued/control.lua:20: in function <__Todo-List-Continued/control.lua:19>

and

Le mod ✔ Todo List - Continued (20.0.2) a engendré une erreur non récupérable.
Merci d'informer l'auteur de cette erreur.

Error while running event Todo-List-Continued::onluashortcut (ID 37)
Todo-List-Continued/todo/features/exporttask.lua:6: attempt to index global 'global' (a nil value)
stack traceback:
Todo-List-Continued/todo/features/exporttask.lua:6: in function 'updateexportdialogbuttonstate'
Todo-List-Continued/todo/ui/mainframe.lua:57: in function 'createmaximized_frame'
__Todo-List-Continued/todo/features/main_ui.lua:69: in function 'maximize_main_frame'
__Todo-List-Continued/todo/features/main_ui.lua:9: in function 'toggle_main_frame'
__Todo-List-Continued/todo/todo.lua:222: in function 'on_lua_shortcut'
__Todo-List-Continued/control.lua:43: in function <__Todo-List-Continued/control.lua:42>

when a client clic to task or add task in MP

Got the exact same error. I tried to reproduce: Created a task with 3 subtasks - handling without any problems.
Saved the game, exited Factorio and reloaded. The error now occurs when opening the todo list (using the button at the top left.)

Sigleplayer, slightly modded. ( About 30 mods).

I have no experience in modding or bug reporting, but I am available to answer questions.

Open your game folder, check the last part of ~/Games/Factorio/factorio-current.log
if you use steam, check about %appdata%/Factorio/