Using vendored_frameworks did the inclusion as @Keith said. But the addition to his answer is that I added the custom framework as a 'Do Not Embed' option. and the pod was able to link it and provide it to the using Application.

You can also provide more frameworks. The following line includes Custom. framework nad Custom2.framework frameworks and any Xcode framework .xcframework
s.vendored_frameworks = 'YourOwnFrameworksFolder/Custom.framework' , 'YourOwnFrameworksFolder/Custom2.framework', 'YourOwnFrameworksFolder/**.xcframework'
Also, if your Custom.framework needs another framework to work successfully, I think you will need to provide it also in the vendored_frameworks but you don't need to embed it in your pod framework project as the pod project itself does not use it directly.
So for example, if Custom.framework needs CustomDependency.framework, the vendored_frameworks will be :
s.vendored_frameworks = 'YourOwnFrameworksFolder/Custom.framework' , 'YourOwnFrameworksFolder/CustomDependency.framework'