Thank you. I'll check that out next time I reboot.
I'd tried the Fn and also a few other search suggestions I came across such as holding down both FN and Esc to reset.
iirc they used to work fine, but other Fn shortcuts in say Excel no longer work either... it may have started after I installed updated software for my keyboard/mouse. Supposedly the mouse needed an upgrade to a separate app (Logitech Options) whilst the keyboard continues to use Logitech set point. There are some settings in there to allocate enhanced tasks to each F key, but I have them all set at "default".
F5 now
sometimes opens Microsoft Edge, (which I never use) and at other times appears to do nothing. F1 opens Microsoft Word (rather than help) F7 opens Firefox (my default browser) if Im using another prog. Everything seems to have got all mixed up.