The most common and most likely answer to this crossword clue is the 5 letter word THOSE
I've seen this crossword clue in The Guardian
T
H
O
S
E
More clues leading to the result THOSE
- That group of map-makers featured in article
- Some specified article plugged by seaman
- He’s to be changed, not these
- That group shows spirit, first to last
- The less obvious code with letters cycled
- Big breakthrough, article is for them
- Many that can be obtained from the external operating system
- Merchant finally stocking this and that
- Demonstrative term from character, first to last
- d Distinctive character of individuals cycling? Not these people!
Buddy explains!

The straight part
We know that "not these" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not these = those.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does THOSE mean?
THOSE pronoun- (demonstrative) The thing, person, idea, quality, event, action or time indicated or understood from context, especially if more remote geographically, temporally or mentally than one designated as "this", or if expressing distinction.
- The known (thing); used to refer to something just said.
- (demonstrative) The aforementioned quality or proposition; used to emphatically affirm or deny a previous statement or question.
- (relative) (plural that) Which, who; representing a subject, direct object, indirect object, or object of a preposition.
- Used in place of relative adverbs such as where or when; often omitted.