The macOS deployment target ‘MACOSX_DEPLOYMENT_TARGET’ is set to 10.11, but the range of supported deployment target versions is 10.13 to 13.1.99
When installing certain plugins (e.g. Firestore) that require a minimum deployment target that is higher than the one set in the Xcode project, this issue can appear:
The macOS deployment target ‘MACOSX_DEPLOYMENT_TARGET’ is set to 10.11, but the range of supported deployment target versions is 10.13 to 13.1.99
To address this, open the macOS project and set the minimum deployment target as needed:
It's also a good idea to have the same target in the Podfile (first line at the top):
platform :osx, '10.14'
Note: Since Flutter 3.7, the minimum macOS version supported by Flutter increases to 10.14 Mojave.
Resources
Also note my answer on StackOverflow about additional changes in the Podfile: