Apologies if I am using wrong etiquette and/or protocols. Please let me know.
You are doing fine. Since you mention it, though, and you are new to us...
The etiquette "rules" are
(a) no abuse of other members, with or without vulgar language - though we certain can and do make little jokes with each other sometimes.
(b) don't post on another forum to get a second opinion without telling us and posting a link to it. This is called cross-posting and it wastes our time unless we, too, have drawn a total blank.
(c) communicate. Don't say "this doesn't work" but fail to tell us what it DOES do and why that differs from what you expected. We aren't mind readers and I lost my crystal ball while on vacation a couple of years ago.
Protocols include giving us time to think before we answer, since we are literally all over the world from almost every populated time zone. When you post, we might be sleeping. Arnelgp, for example, is from the Philippines. I'm from south Louisiana, USA. Bob Fitz is from or near London. You are from or near Edmunton, Alberta, Canada. We've got folks from every continent except, perhaps, Antarctica. Remember that we are all volunteers, just paying forward the help that we once got - and often STILL get from the other members.
You CAN disagree with us and pursue the disagreement. You CAN tell us you don't understand and ask us for clarification. I'm letting YOU know that you are doing fine so far.
NOW... as to populating multiple fields from a combo box,
Office VBA reference topic
learn.microsoft.com
So far, I got recommendations to write VBA but to me I would think this should be a basic function of Access.
It is and it isn't. You could in theory bind the combo box to the bound column designated from that box's .RowSource and that would work. The control's .Value property comes through that mechanism. In fact, when you build the combo box with a wizard, that linkage is one of the three choices that the wizard offers you. It can easily set that up for you. However, only one column from the .RowSource can be the "bound column" so copying one column's value is a basic function of Access. Multiple columns are not automatic.
Office VBA reference topic
learn.microsoft.com
The solution might be as simple as remembering that the value of the combo box is selected when you click on that value. Therefore, in your control's
controlname_Click event, you could copy the OTHER columns.
Office VBA reference topic
learn.microsoft.com
Just remember that in Access and other MS Office members, most collections are zero-based, not 1-based, so the first column is
controlname.Column(0) and the last of n columns is .Column(n-1).