What deployment target have you selected for your app ?
Read this if you need explanation:
This second SO gives a lot of solutions to address the problem directly by adding the missing files.
This other seems simpler to use:
According to the Xcode Wiki, v10.0 supports iOS 12.0
12.4 requires Xcode 10.3
I was looking for this wiki page, cannot find the link. I googled, unsuccesfully.
Have you kept ?