Why am I getting this error all over the project? Can anyone help solve it?

You have a link error, but your screenshot does not show the actual error.

To find the actual error, press Cmd-9 in Xcode to open the report navigator. The report navigator will let you see all the build steps in your project. You may find the following article helpful:

https://www.swiftdevjournal.com/why-wont-my-xcode-project-build/

When you find the actual error, reply in this thread and paste the text of the error message. Without the error message no one here can give you any more help.

The usual causes of link errors are forgetting to include a framework and using the same name for a class or struct in your code that is in one of the frameworks your app links to.