At last! Discotheque Of Doom ins running for me...

[aquaMat]

@ Rob & brell:

Thank you both for your comments. I can see clearly now.
I'll try to log-out from my old Mac, so I then can stay logged-in from my MacBook, as I'm using that much more often.

However, that

update session

feature seems a quick + easy solution too - I have never tried that... not once in all those years.
Maybe I will try that right away now - just to see how it works.

Thanks !!