When entering text edit mode by double-clicking a text item, all of the item's text should be selected
Musescore 3.5.2, on Windows 10.
Currently, when double-clicking a text item on the canvas, MuseScore will position the text cursor under the mouse without selecting any text. Double-clicking a text item, and then starting to type on the keyboard, will insert new text rather than replacing the existing text. In order to replace the existing text, the user needs to triple-click instead.
Inserting new text is almost always undesirable when editing small text items like dynamics, chord symbols and fingerings. I suggest that the canvas should automatically "select all" when entering text edit mode for this type of text item.
For consistency, it may also be sensible to "select all" for larger text items such as stave text and page titles.