In my case, I'm developing a Framework that uses 3rd party Swift Packages internally. Originally, I thought this error was being thrown because I upgraded to Xcode 15. Turns out, it was completely unrelated. If you are using 3rd party libraries and want to export a Framework, you must include the "@_implementationOnly" tag in front of the imports. Example: "@_implementationOnly import BoltsSwift". If you do this, it will not include these 3rd party library imports in the binary modules within the framework. This is great because the users of your framework don't care about the 3rd party libraries used in the back-end. Hope this helps at least one person! I rarely see anything online about the @_implementationOnly tag.

Many of these replies may be truthful, but it seems like there are some inconsistencies. It works for some people and it won't work for others. In my case, I'm developing an SDK that uses 3rd party Swift Packages internally. Originally, I thought this error was being thrown because I upgraded to Xcode 15. Turns out, it was completely unrelated. If you are using 3rd party libraries and want to export a Framework, you must include the "@_implementationOnly" tag in front of the imports. Example: "@_implementationOnly import BoltsSwift". If you do this, it will not include these 3rd party library imports in the binary modules within the framework. This is great because the users of your framework don't care about the 3rd party libraries used in the back-end. Hope this helps at least one person! I rarely see anything online about the @_implementationOnly tag.