global trill line setting

Is there a global setting to disable trill lines, so that every trill does not have a line?

Yes there is. In Engraving Options (Cmd/Ctrl + Shift + E) select the Ornaments section and choose not to show the extension line.
That is then your default for that project.

There is a ‘Save as Default’ button at the bottom if you want to save that for all projects on that computer.