Because project depends on flutter_localizations any from sdk which depends on intl 0.16.1, intl 0.16.1 is required

You need to upgrade your flutter version on your local machine to flutter 2.0+ now cause you are importing null safety supported dependency which uses dart sdk 2.12.0 but you have 2.7.0 which is making conflict with the other dependencies. If you do have 2.0+ already then upgrade the sdk of your app from pubspec.yaml. You will then have to update your code to full sound null safety starting from upgrading all the dependencies then the code, its not that hard even if your app is using firebase I get my apps upgraded to null safety within a week. Once all gets sorts out you'll have no trouble with your project in importing some null safety dependency or some else more importantly you will be able to have better performance of your app and can keep all the dependencies to support latest versions and might possible you app will be android 12 ready too