What @Criggie said because there is no adjuster on these derailleurs, as you have discovered.
Additionally, I find it possible to get gears working without an adjuster, or with the adjuster screwed all the way in - after all, Shimano have done the hard work already in engineering. You would set the high limit screw so the guide pulley is perfectly in line with smallest cog and then attach the cable so that it is tight, but nothing excessive. This works if the derailleur is nicely aligned and the cable has been pulled carefully or ridden so that the housing is 'bedded in'.
This way gives you maximum adjustment later, or if in a real pinch and no barrel adjusters are present at all, a way to set it up for now until sourcing an in-line adjuster. It's what I do now when setting up derailleurs, not least because it gives confidence that the high limit screw is properly set while also giving a neat look.
It works as well for the front derailleur but those are a little more sensitive, still works though if all is aligned well. You might try the 'hack' of setting the L limit screw a little tight, attaching the cable and then relaxing the limit screw back into place but be careful not to mash the cable by doing too many iterations.