How is the form that's opened determined? What are you selecting in the combo box? If it's just that you want a list of forms in the combo box, then that's easy. Otherwise, yes, I would do what you suggest: make an IF THEN block (or a SELECT CASE statement) in VBA and open the appropriate form. Tell me exactly how this form is chosen and I'll help you out. I haven't done anything like this in any of my classes, but it would make a cool TechHelp video.

In my table [TBL_Patients], I have a combo box field named [Cover_RX].  For context, Cover Rx is a medication discount program.  The combo box selections for that field is either "Yes" or "No".  Basically, I document if each patient enrolled into the discount program or not.  On the after update event, if "Yes" is selected, I'd like the popup form [FRM_Cover_RX_Yes] to open.  That form gets it data from the table [TBL_Cover_RX_Yes].  There are several fields in that table allowing me to document information that a pharmacy would need so the patient could get his/her discount on meds.  If "No" is selected, the popup form [FRM_Cover_RX_No] would open with a field allowing me to document why the patient does not have this discount.
I use this in the "where condition =" line in my macro to ensure that info is documented on the right patient: ="[Patient ID]=" & [Patient ID]

Yeah this would be a simple AfterUpdate event:

If ComboValue="Yes" then
   DoCmd.OpenForm "Form1"
else
   DoCmd.OpenForm "Form2"
end if

Assuming your combo box is storing the text value "Yes" and not an actual Yes/No field, which case you'd change it to True/False. Is this data stored in the same table as the patient info, or is it a different table? I ask because you might be better off just showing/hiding relevant fields instead of opening two entirely different forms.

my combo box is actually storing the words "Yes" and "No".  I prefer that over a check box (True/False).  The Yes/No is in the same table as the patient info.

The Cover Rx details is in it's own table

The reason for no Cover Rx is in it's own table.

So, 3 tables total.  I've always been under the impression that it's not a good idea to have a table with a bunch of empty fields so that's why I created 2 different tables for the cover rx details describing the yes/no.  not sure if that's the best approach.

In my relationships, the patient table and the cover rx yes table are connected via a one to many and the patient table and the cover rx no table are connected via a one to many.

The way you're doing it is fine. If it's just ONE empty field, or a couple, that's not a big deal. For example, let's say you have an OrderType which is either Online or Shipped. If someone selects Shipped you could just hide (Visible=FALSE) the Address fields. Sure, you'd have a blank couple of fields for each customer, but that's not too big of a deal. If your "No Cover Rx" for example is just ONE field, there's no reason to have a separate table for it. Just my opinion though. If what you have works, keep it.

And of course, I've got TONS of Developer lessons available to teach you programming. If you just want a quick intro, start here: Intro to VBA. It's free.

I wasn't sure how to incorporate the where condition "="[Patient ID]=" & [Patient ID]" into the code that you wrote, so I created a macro that mirrored what you wrote so I could add the above where condition.  yes...it's time I take I start learning VBA.