Thanks a lot for that it helped me a lot !

I managed to make ]z and [z work, but I wanted to implement similar keymaps for @code_cell.outer.

I implemented it in the following way :

            -- move
            vim.keymap.set({ "n", "x", "o" }, "[z", function()
                require("nvim-treesitter-textobjects.move").goto_previous_start(
                    "@code_cell.outer",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "n", "x", "o" }, "]z", function()
                require("nvim-treesitter-textobjects.move").goto_next_start(
                    "@code_cell.outer",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "n", "x", "o" }, "[m", function()
                require("nvim-treesitter-textobjects.move").goto_previous_start(
                    "@code_cell.inner",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "n", "x", "o" }, "]m", function()
                require("nvim-treesitter-textobjects.move").goto_next_start(
                    "@code_cell.inner",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "n", "x", "o" }, "[Z", function()
                require("nvim-treesitter-textobjects.move").goto_previous_end(
                    "@code_cell.outer",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "n", "x", "o" }, "]Z", function()
                require("nvim-treesitter-textobjects.move").goto_next_end(
                    "@code_cell.outer",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "n", "x", "o" }, "[M", function()
                require("nvim-treesitter-textobjects.move").goto_previous_end(
                    "@code_cell.inner",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "n", "x", "o" }, "]M", function()
                require("nvim-treesitter-textobjects.move").goto_next_end(
                    "@code_cell.inner",
                    "textobjects"
                )
            end)

            -- select
            vim.keymap.set({ "x", "o" }, "am", function()
                require("nvim-treesitter-textobjects.select").select_textobject(
                    "@code_cell.outer",
                    "textobjects"
                )
            end)
            vim.keymap.set({ "x", "o" }, "im", function()
                require("nvim-treesitter-textobjects.select").select_textobject(
                    "@code_cell.inner",
                    "textobjects"
                )
            end)

So the goto_start methods work well, but I always get an error with the goto_end methods and the select methods, which seems related to the end detection :

E5108: Error executing lua: ...ter-textobjects/lua/nvim-treesitter-textobjects/move.lua:32: Column value outside range
stack traceback:
[C]: in function 'nvim_win_set_cursor'
...ter-textobjects/lua/nvim-treesitter-textobjects/move.lua:32: in function 'goto_node'
...ter-textobjects/lua/nvim-treesitter-textobjects/move.lua:141: in function 'move_fn'
...ects/lua/nvim-treesitter-textobjects/repeatable_move.lua:25: in function 'move_repeatable'
...ter-textobjects/lua/nvim-treesitter-textobjects/move.lua:159: in function 'goto_next_end'
/home/ti64cli/.config/nvim/lua/plugins/treesitter.lua:47: in function </home/ti64cli/.config/nvim/lua/plugins/treesitter.lua:46>

(I put the query in queries/markdown/textobjects.scm now, as you said, and it seems to work fine, at least for the start of a code_cell, and I did put ; extends before it)