The version of top in bookworm seems to have changed the processing of
the <space> keybinding for :Refresh-Display, and you can see it
immediately drawing the screen *twice* while registering the current
`top` process as something taking 100% of the CPU.

The former behaviour was to just trigger the timer right now, and
calculate the resource usage and refresh.  This was useful.  The new
behaviour is to calculate resource usage, refresh, wait 0 seconds,
calculate resource usage (funnily enough, the only thing to take CPU
since 0 seconds ago was top itself), and refresh again.  This is not
useful, because it hides the behaviour of the rest of the system,
which had only a tiny chance of being scheduled in those timeslices
where top was recalulating if they were using anything less than 100%
of a core(s).

Tested on a vanilla system just case I had done something funky in
.toprc.  manpage doesn't seem to deal with reverting to previous
behaviour, and doesn't mention any change in how <Space> or
:Refresh-Display may have been changed.