Is there anything in the synastry or composite chart that indicates how a couple first met?
I can only speak for myself...but I am not aware of any aspect or configuration in the overlay or composite chart which can tell you how a couple first met, and I don't think there is any aspect or configuration which is that specific. Astrology deals in potentials, not absolutes. The only possible exception might -- with emphasis on
might -- be a chart based on the day the couple first met in person (but many couples don't remember on what date they first met, never mind the time). This will probably not tell you much (if anything) about the specific environment in which the two people met -- school, work, etc. -- but can sometimes tell you what motivations and/or expectations they were bringing with them at the time. Comparing each person's natal chart to this chart can potentially also tell you what sort of impact the first meeting had on that person -- such as which one was more profoundly affected. An article which describes this in greater detail can be found here --
https://cafeastrology.com/relationshiptimingastrology.html
An individual's natal chart can offer some clues regarding what kind of romantic partner he or she is more likely to be attracted to and/or where he or she is more likely to find a romantic partner. As an example, the seventh house is the house of long-term partnership. The sign in which a person's seventh house cusp falls is often an indication of what kind of partner they most hope to attract -- and when an individual's seventh house is activated by a prospective partner's inner planets, this is often a significant indicator of attraction. The sign and house in which Venus (for a man) or Mars (for a woman) is found can also be an indicator of what kind of partner this person finds most desirable. The placement of the seventh house ruler (the planet which rules the sign of the seventh house cusp) can potentially offer clues regarding where this person is most likely to meet a romantic partner.
In my case, my seventh house cusp is in Gemini, which is ruled by Mercury -- and one thing which I definitely need in a partner is intelligence. (If a man can't hold a conversation with me, it doesn't matter how good in bed he is -- I will get bored and lose interest very quickly.) My Mercury is in Gemini and is in my seventh house, as is my Mars -- according to my natal chart, this seems to suggest that social events and especially those associated with culture and the arts would be the most likely places for me to find a partner especially since this placement also suggests that I want a partner with good manners and refined tastes (which I do). Since the seventh house is the house of partnership, another distinct possibility for finding a prospective partner would be a social event specifically targeting singles since these are events which are all about partnership.