Glide has no knowledge of google sheet specific functions like a dropdown in the sheet. It’s simply a database of data, so it’s reading and writing data to a cell. Not making a choice in a dropdown. Technically you could have Glide write anything to that cell irregardless of what the options are in the sheet dropdown.
You can create a dropdown in the app with a choice component if that’s what you need. You have to set it up yourself though. Glide can only make a best guess basic layout to get you started. The rest is up to you. You can customize any of the components and add or removed them as you need.
I don’t know how you have manychat integrated in your set up, but it’s important to know that glide will not trigger any onEdit event when data edits come from Glide. Only onChange events get triggered. I don’t know if this is the case as I don’t have any experience with manychat or integromat. Just a thought at this point.