Right : I double checked what I did on my server. Turns out I did this way :
yum --setopt=obsoletes=0 install nextcloud-17.0.2-1.el7
yum --setopt=obsoletes=0 install nethserver-nextcloud-1.8.4-1.ns7
NB : you might enclose console output in a code block (see toolbar) to make it more readable.