Hey Tony,
Unfortunately, at this time this still requires editing a bit of core plugin code, which means that the change will be lost after the next update 🙁 But, I have made a development ticket for us to add a filter here, so hopefully we get that into the next release anyways (which would make this super easy to change! 🙂 )
For now, what you’ll want to do is head your Community Events plugin files and head to src/Tribe/Main.php there.
Once in this file, about 3/4 of the way down around line 1922 or so, you’ll see a function called formCategoryDropdown(), the one originally referenced in that thread you shared above.
Look for a line of code in this function that looks like this:
$shown_item_count = 9;
Simply change that 9 to 20, or 30, or some other high number like 99 or something, then save the file and it should show all the categories that exist.
I hope this helps!
Cheers,
George