Hi Tony, thanks again for your help.
My main issue is that at present time I have lot of devices installed with this SW version, so I should further investigate if I can use the old Linux version.
However, great news, it seems I found what snap I should download:
core18
core20
gnome-3-28-1804
gtk-common-themes
snapd
ubuntu-core
xibo-player
I will perform some test, I will tell you and the community what happens.
Thank you for your help and your advices.
Best regards
Giovanni