With editor after initial submission My manuscript appears online as " with editor" for 65 days after initial submission in one of the top journals in my field. Could this be because of the Summer vacations? Should I wait till 15 September  or should I send  immediately an email enquiry?
This can be for many reasons, and certainly one of them is that everything is slow because of summer vacations.

Another explanation is that the Editor cannot find qualified reviewers to evaluate your manuscript, or s/he found reviewers but they did not accept the request yet (again, possibly because of summer vacations).

I suggest to send a gentle mail to the editor (preferably using the editorial manager platform) to say that in case the delay is caused because they are unable to find experts, you will be happy to provide a list of those (be sure that you indeed have few in mind). Thank her/him for considering your paper for potential publication and wait. Do not forget to add in the loop your co-authors.

You do not need to wait more, 65 days seems a lot.