T-Mobile is the latest carrier to roll out One UI 3.1 to the Galaxy S10+
SamMobile reports that the update also includes the March security patch, as well as improvements to camera performance. Furthermore, the changelog mentions that the “overall device performance has been improved” too, along with the security of the phone (thanks to the March patch).
If you'd like to update to One UI 3.1, you should be looking for firmware version G975USQU5GUCG. Keep in mind that while the update shouldn't affect your personal data, you might want to back up your data if you have anything precious stored on the phone.
Nothing else to add, just that the other Galaxy S10 series phones should get the One UI 3.1 too. It will let you add a handful of effects during video calls, as well as remove private data from photos before you share them.