In addition to using the mouse you have some keyboard shortcuts:

• Spacebar: Play/pause toggle.
• 1, 2, 3: Speed (paused, normal, fast)
• ⭠, ⭢: Speed decrease/increase.
• ⭡, ⭣: Bottom menu decrease/increase (hide, show, locked)

A thing it took me a long time to notice is that you can delete a whole line by clickign on its circle in the bottom menu, and then click the '🗙'.

• Mini Metro - All Levels and Achievements, by Drawing Dead - Includes a good starter guide.

• Eye Sigil - Secret stage, part of an ARG that spans multiple games:
  • https://wiki.gamedetectives.net/index.php?title=Eye_Sigil_ARG
  • https://steamcommunity.com/sharedfiles/filedetails/?id=440627793
  • https://mini-metro.fandom.com/wiki/Hidden_Map

• blueeyedrat.itch.io/mini-metro-map-pack - I think these are all also available via Steam Workshop.
• kucnjnj.itch.io/mini-metro-more - Ditto.

• Mini Metro - Workshop Guide.
• Map Making Shape/SVG Tool.
• richvreeland/mini-metro-audio-toolkit/.
• Mini Metro: Building Your Own City Soundscape.