how do I open an application

I am guessing the User has Assigned the Default Web Browser to something other than the Builtin Safari Web Browser ?

Further and maybe a URL was sent in an e-mail and when you click on it the Error -10673 is presented ?

If so, two options as I see it.

1 - Make Safari the Default Browser again

2 - Refer to below and Right Click on the URL and Choose Firefox or whatever is the " Other " Installed Browser

That would indicate an issue with that particular app. Which app is it exactly? Was this app working before?

Have you tried downloading and reinstalling the app? Maybe a newer version is required.

You are very welcome and thank you too 👍