Wanted to make an individual post addressing this considering it's been inquired about since the beginning of the MM26 season.
After a recent app update went live yesterday, we now have the ability to upgrade all of our eligible Player Traits with a single button. Previously, you would have to select each eligible trait individually and upgrade them one at a time. So this is a nice quality of life update that has been suggested by the community since the beginning of MM26 when traits first launched in-game.
To see this change, you'll need to first make sure your app has been updated to the latest version via your App Store. Then, navigate in-game to Trades -> Player Trait Upgrades -> Upgrade to put this new button into action.

