Terminal-Job and Terminal-Normal mode
When the job is running the contents of the terminal is under control of the
job. That includes the cursor position. Typed keys are sent to the job.
The terminal contents can change at any time. This is called Terminal-Job
Use CTRL-W N (or 'termwinkey' N) to switch to Terminal-Normal mode. Now the
contents of the terminal window is under control of Vim, the job output is
suspended. CTRL-\ CTRL-N does the same.
In Terminal-Normal mode you can move the cursor around with the usual Vim
commands, Visually mark text, yank text, etc. But you cannot change the
contents of the buffer. The commands that would start insert mode, such as
'i' and 'a', return to Terminal-Job mode. The window will be updated to show
the contents of the terminal. :startinsert is ineffective.
So, you can do
Or, though it isn't mentioned in the quoted section,
<C-w><C-w> cycles through windows even when started from Terminal mode.