Regarding using multi-value fields to create a combo box with checkboxes, I did something like that in my movie collection database (picture below).  The caveat is that a multi-value field must reside in a table.  If you avoid using MV fields in your database like many of us do, then you most likely have to create a dummy table with a MV field, which was what I did.  In other platforms, like SQL Server, .NET, etc., where MV fields don't exist, a combo box like this must be done in some other, more complicated ways.  One way is to create a fake combo box with a fake form or grid that has checkboxes.

Yeah, creating a dummy table to store the filtering settings is exactly what I did, but shh, don't give away all my secrets. I got puppies to feed. LOL. :)

Another way to do this is to create a "fake combo box" that is a continuous form, which allows all kinds of formatting as pictured below.  This trick you did teach us, in this YouTube video from 2020:

     Can you have a List Box or Combo Box with Formatting and Colors in Microsoft Access?"
     https://www.youtube.com/watch?v=FET8JG8w4Xg

Yeah, I taught the basic trick of using a continuous form as a "fake" list/combo box in that video, but I don't think that database in your screenshot is mine. My example was just about getting different colors and formatting in the list.

I don't remember ever doing one like that with checkboxes, flags/images, and multiple selections inside the fake combo box. I searched through my old stuff too and couldn't find one. So I think the general continuous-form trick came from my video, but that particular implementation wasn't one that I built.

Richard  Sorry for the confusion.  That was my work, but based on the idea you taught in the video: a subform disguised as a dropdown or list box.  (Also, the form footer can be used to place the OK and Cancel buttons, making it look just like the one done with multi-value fields.)

I wouldn't mind you doing another video on this.  This trick is often used in other environments too, such as web app, Power Apps, etc., because the built-in features often don't allow much formatting.  You often have to create fake panels, frames, or what not, and disguise them as something else.

Yeah, I like what you did with the flags there. Maybe I'll add it to the list.