When clicking the 3 dots editor button in a field, it pops up the Text Editor as usual and in most cases it will say how long the field currently is and the max length of the field. e.g. it may say '13 characters. (Max: 50)' but if the field has a NULL value it will say 'lblTextLength' when it probably should say something like '0 characters (NULL)'.
HeidiSQL Version 9.3.0.4984 x64
Hopefully this hasn't been reported before and isn't a duplicate.