Can you upgrade the horse in Elden Ring? Like upgrading its health/vitality, stamina, other stats...
Torrent's status is synchronized with player status. The player's stamina gauge is reduced when dashing while riding, for example, which is most obvious during cavalry combat.
The game's system does not reduce stamina except during combat, so it's more accurate to say that you only see it during combat.
So, technically you can upgrade Torrent's status, but not specifically.