Sorry for the Fill troubles! I assume you're talking about the dropdown arrow for the "Choose a Quick Fill" menu? When I load the Fill Envelopes page in Safari I'm able to see the dropdown, so I wonder if it might be related to the specific browser version or settings you're running?
Would you shoot us an email at email@example.com with 1) your Goodbudget email address, so we can see if it's an issue specific to your household, 2) a screenshot of the Fill Envelopes page where the dropdown is missing, and 3) the details of what version of Safari you're running? That would better help us identify and understand the issue you're facing. Would you also try logging into Goodbudget in another internet browser and seeing if the issue still occurs there?