You can reset Registry Editor (REGEDIT} window position, size, etc. to its default settings in Windows 11/10. To restore it, use the Reset option.

The second way is to use the Registry Editor to delete a value citing the current width of the navigation pane. Reset Explorer navigation pane width to default ...

Switch from File Explorer to an alternative like XYplorer or OneCommander—and set the alternative as the default, with the help of a registry hack.