In the calendar view you can click on the guests reservation. When the info pops up on the RIGHT hand side of the screen it will give you the ability to enter private notes (your own notes about the guests).
Sadly this is specific to a reservation and not (currently) to an Airbnb profile. There are some PMSs that allow you to "make" guest profiles. You can also download your guests as a CSV and loadthat into a spreadsheet (to make it easily searchable). I am not completely sure of a way to make this scalable outside of setting up some sort of Zap.
All of that being said, I would make sure to mention it to the guests with some sort of message like "I hope to host you again in the future!! If there is anything that I can do to make your next stay more enjoyable (all linens and towels in one room, more pillows, ect) please don't hesitate to reach out ahead of time". This way you aren't assuming/ calling out things about their personal life and are instead inviting them back with an open line of communication.
Upfish Management - Vacation rental property management in Atlantic City