How do I set default applications in Ubuntu?

To set the default application for a specific file type, locate a file of that type in the file manager, right-click it, and select Properties. Click the Open With tab and select the application you want to use for that file type. Use the Set as default button to make the application the default application.

How do I set default apps?

On the Start menu, select Settings > Apps > Default apps. Select which default you want to set, and then choose the app. You can also get new apps in Microsoft Store.