writing without time signature

When writing without any time signature, how can I choose the grouping of notes in order not to have an infinite row of quavers or semiquavers (or even less) all bound together?

You can invoke the context menu at any time (ctrl/cmd click) and Beaming>Beam together or Break beam or split beam.
You can also assign keyboard shortcuts to Beam together (I chose cmd-B) and break beams (alt-B on my French layout keyboard) or split beams (ctrl-alt-B). IIRC, there’s no general option in this case.

You’ll indeed have to manually beam, or you’ll have to type in complex time signatures (3+5+2/8) and then hide them. What you are doing may dictate the better approach. Of course, if you’re strictly against barlines appearing at all, then the former option will be the way to go.

thank you for your answers. I’ll try everything……