Oxford Dictionary (https://www.lexico.com/en/definition/just) gives a bunch of definitions about “just”
there are 3 sub-items in 4th item, one of them is pointed out by blue rectangle in the following image.
What is the relationship between the sub-items and the main one?
Could all of 3 sub-items could be a piece of meanings of "Simply", I guess not.
sub-item 4.2 gives
Used as a polite formula for giving permission or making a request.
and gives this example
just help yourselves
if this is one piece of meanings of the main item, namely, "Simply", the following sentence would sound normal
Simply help yourselves
which actually sounds uncommon, any ideas?
Besides, neither Oxford dictionary (https://www.lexico.com/en/definition/simply) nor Cambridge dictionary (https://dictionary.cambridge.org/dictionary/english-chinese-simplified/simply) has a piece of meaning similar to this one (shows politeness).