Hello，jaydonx33472
Thank you for posting in the Microsoft community.
I see that you want to specify the default application to be opened for a specific type, you can choose "Start > Settings > Applications > Default applications", in this page you can set the default value for the file type or link type, or set the default value for the application.
Then I see that you can't find the corresponding application when you click on the application icon on the taskbar, please check whether the file exists according to the way as shown in the picture, then select the corresponding application, right-click it and select "Create shortcut", then drag it to the taskbar to try it.
If you encounter this problem with every icon, or if the problem still exists with the above methods, you can create a new account, log in to the new account, and see if the problem persists. If the issue doesn't occur in the new account, or may be related to the original user settings or configuration file, follow the steps below: Create a local user or administrator account in Windows - Microsoft Support
If you need further assistance, please let us know the issues you encountered during the operation, and we will provide you with more advice.
Best Regards，
Rota|Microsoft Community Support Specialist
