Company brand rules often specify particular fonts, or it may just be that you have a particular favorite font. Either way, if you subscribe to either the Pro or Team plans then you can upload your own custom font to Xara Cloud.
If you are an Admin, then you can upload custom fonts via the Admin Panel. Admins can reach the Admin Panel by clicking the team name (top left of File Picker - MyCompany in this example) and then More team settings.
Then in the Admin Panel click on Custom Fonts on the left. Click Upload team font and select the font you wish to upload from your computer. You can upload multiple fonts at a time by holding Shift or Ctrl and selecting. The fonts will upload and be ready for use in your documents.
You can setup your Brand to use your new fonts and apply that Brand to your documents.
Even if you don't want to use a particular Brand, you can select the font from the Text Properties panel (click on any text in your document, the Text Properties panel appears on the right hand side, follow the > to see more fonts). Your imported font will appear under Team Fonts.
Clicking Add team fonts here is an alternative route to the Admin Panel where you can add more custom fonts.