Thanks. I have first tried the method given by Sir @Joan_Sparky:-
So, I have copy / pasted Lib-1, from old project-1, into my current project-2 folder, where Lib-2 was already there.
But I was not able to ADD it. So Lib-1 is still not visible in project-2 library list.
Though via the "footprint editor", I was able to add a 'footprint" from Lib-1 into Lib-2 successfully.
Yet the full Lib-1 could not be ADDED, to project-2, even though the folder Lib-1 is copied there.
I don't know the steps to add it.
That part above, I could not do. Once I had added a library selecting the "global library" option, ..but then I had trouble & error involving that library. So I am shy to attempt that. (May be I did not do the precise steps?)
(However, by being able to copy the "footprint" only, from the old Lib-1, into Lib-2, my present problem was solved 90 %)
That is interesting too, & next, when I start a New Project, I will study, and try to do it the "template" method.