Share Home between 2 releases

[Grizzly]

Hi all

I'm sure this is simple (once you have done it) I did search and found many 
opposing instructions (even within AskUbuntu)

On one box I have three drives/OS's (Win7, LTS Ubuntu & Latest latest Ubuntu), 
I would like to share (if safe) one ~Home (dir not partition) between the 
Ubuntus (18.04.5 & 21.10 Unity at present) 

It seems a total waste to have much the came content in both Homes

pointers and/or warnings please, will Gnome / Unity mix be a problem?

Thanks