How is it not true? If a site is saying for example, “password must be less than 20 characters” – that is purely a limitation based on the size of the database field, which you can only assume it’s being adding to that field as plain text. A hash will always be the same length and password length would not matter.
Of course, requiring at least one symbol or upper case letter etc is a good idea, along with a minimum length. Many websites won’t let you use a password longer than a certain amount of characters. The only reason for that limitation is that they are storing the database field as plaintext, and anything longer will not fit into that column.