This answer does almost have what I need.
But it's two years old and nothing in the links provided in the answer points to a solution for EE3.
I want another save / save + close button pair on top of the entry as I am editing very long entries with many fields.
Does anybody have a working solution for EE3?
Can I use i.e. the plugin Publish Bar which has been last updated in 2011? Did the EE plugin API change a lot since then?
I don't want to alter the backend code, as that would be a lot of work for each time I need to update EE3.