Yep, this is very easy…
2 main options, depending on exactly what you need…
The first way is simply to have a ‘Notes’ field on whatever datatype you need it on, of type ‘Text’, which is a list. Then simply add a new note (text) to the list whenever a user creates one.
The second, slightly more complicated (but ultimately better), way is to create a Datatype of ‘Note’, with a text field for the notes, a User field for the User, and custom datatype fields to link it to whatever other datatypes you need it linked to.
That way you can store much more information about each note, such as when it was made, by who, what it relates to, and anything else you might need.
It might be useful to then create a ‘Notes’ field on the connected datatype(s) which is a list of Notes, but that would depend largely on the anticipated number of notes each data entry will likely have (if it’s hundreds, or more, then I wouldn’t recommend that, but if it’s a few dozen or less then it’s probably a good idea.).