Thanks for trying it and for the clear step-by-step feedback! No extra step should be needed: the Channel Rack opens below the arrangement, so the Drum and Piano tracks remain visible above it.
I checked the City Bounce flow and found the edit action was hidden until hover, with the controls shifting as they appeared. I have updated the browser beta with an always-visible Edit button beside each pattern. Open Patterns, then click Edit beside City Drums to reach its steps. I have verified that route on the live itch build.
Please try again after reloading the page and let me know whether the rack appears. If it still does not, a screenshot and your window size would help me investigate. This kind of first-session feedback is exactly what I need. Thank you!