hey @Frenchy_Devs -- someone else asked about exactly this yesterday. See post here:
All you need to do is add ; formatter=items -> join(items, "BLAZE_AND") to the end of your current formmenu, after multiple=yes and before the closing }
The suggestion of using the formatter=... in my previous response changes the dropdown menu itself.
If you're re-stating the values of the dropdown menu elsewhere using a formula, like you are with {=choices}, then you need to use that "join" function again.
Below are two examples of how you can do that. I'm not sure which one you wanted so I included both:
{choices=["choice1", "choice2", "choice5"]}
Separate every selection with "or": {=join(choices, " or ")}
Separate each selection with a comma except for the last one, which uses or: {=join(choices, "BLAZE_OR")}
In case you want to learn more, when a dropdown menu has multiple=yes, it saves the selections as a list. Here's a guide that details exactly how to turn that list back into a string like I'm doing with the join function above.