Hey there. After the Bungie Name changes went live mid-2020, your in-game name becomes set as the platform name that you first log in with, I assume that's your Steam account. The new Bungie Name system doesn't support most special characters and also applies a name filter, looking at your profile I assume it's the former issue, as there are some characters in your Steam name that are not appearing properly. That is why you've been given a default name. There is not an option to change your name at this time but a name change option will be added relatively soon, 'at or around Witch Queen's launch is the current estimate.