Short answer: no, it’s not possible with Adalo built-in features.
Longer answer: encrypting the messages is only one part of the equation; you need also to be able to decrypt them. There are various algorithms for that, but all of them require that some user key is private and not exposed to anyone. Consequently, you can’t store this key in the database: if you, as an admin, get an access to this user’s key - you get the access to user’s messages. So you need to store this key inside the app itself.
In order to generate keys, exchange them and store them in the app you will need something written in full code (maybe Adalo component can do it, but I’m not sure).
I just want to make sure I protect user data and store it properly. I have built a social app/prototype and it involves users sending each other messages on the app that are being stored in Adalo database. Any tips or suggestions on how to make the app more secure?
IMHO you’d be hard pushed to get any Adalo app approved for medical information as it all needs to be assessed by the NHS (I seem to remember you were in the UK) to allow you to store PMI and there is zero chance Adalo meets the requirements as they are questionably even GDPR compliant. e.g. No list of downstream processors. Who’s their DPO? etc The chances of you even getting the information you need to satisfy compliance to the NHS assessors is pretty low, especially as they will be probably even politically against “upstarts”.
Proof of concept maybe- but you can’t put real data in there.