Read the errors - they tell you why...
Richiede: php-composer(endroid/qrcode) < 2
Richiede: php-composer(endroid/qrcode) >= 1.6.5
Not sure if you need php-comoposer + endroid/qcode or if you can install a package eg
https://pkgs.org/search/?q=php-endroid-qrcodeRichiede: php-pear(PEAR) >= 1.10.1
(Installato: 1:php-pear-1.9.4-5.el6.noarch >>> version not high enough)
Richiede: php-pear(Net_SMTP) >= 1.8.1
(Installato: php-pear-Net-SMTP-1.6.1-1.el6.noarch >>> version not high enough)
So, the working versions are in contribs:
https://wiki.contribs.org/RoundCubeThe latest version isn't in contribs so you are on your own here. You are using the remi-roundcube repo which we cannot be sure will work. It may well break your system.
Basically you have not got the right packages or versions to install this. They MAY be available but you will have to search to find them.
If you can get it to work then let us know and we can look a the Wiki.