F5 does nothing, or AutomationView: Start Simulation runs but the emulator exits within a second.
The emulator needs three things: a .seq file as the active editor, an initial step in that Sequence, and an online Python language server. Any one missing and start fails silently.
.seq open in the visual Sequence editor. If you are in the text editor, run AutomationView: Open Visual Editor.Open the Output panel, select the AutomationView channel, and read the trace right before the failure. A Python traceback means you want Python Server Crash; otherwise file an issue with the log attached.