As a "text editor", in MS Word (desktop), I know you can double-click anywhere and start writing (and rewriting on the same line won't affect the position of other inline "text cells").
As an "infinite grid", there is https://strlen.com/treesheets/, but it is not exactly geared toward your aim (more like a spreadsheet/outliner combo, or "hierarchical spreadsheet").
As an "infinite grid", there is https://strlen.com/treesheets/, but it is not exactly geared toward your aim (more like a spreadsheet/outliner combo, or "hierarchical spreadsheet").