These are the hotkeys / shortcuts currently available in the 2D viewer:
Available in free & 2D viewer
F1-F8 = Widgets from the bottom right corner (Strategy etc.)
Up arrow = Highlight next car ahead
Down arrow = Highlight next car behind
Left arrow = Highlight driver 1 for the current manager
Right arrow = Highlight driver 2 for the current manager
H = Toggle chat history overlay
T = Write a chat message
F = Toggle full detail live timing
Tab = Toggle live timing
2D Viewer only
Mousewheel = Zoom in / out
+ / - = Zoom in / out