fix of the day. change antimatter.yaml, dropdown to true
Can this be the default please. it took me ages to find this.

Not everyone needs a dropdown menu enabled.
How to enable it is written in the theme readme file:

P.S: Put your customized antimatter.yaml file in user/config/themes/antimatter.yaml, so with updates it’s not overwritten

user/config/themes/ didnt exit. i created it, put the file there, which was ignored.

By default user/config/themes/ does not exist, it’s normal. But adding your theme file there should not be ignored (just tested changing the dropdown param value, was applied)