Alot of mock services have come out of the woodwork now due to genAI, but I don't think these are the solution from decoupling your services from cloud providers, because they have to keep up with schema updates for every single service which isn't practical even with genAI.

You should be writing everything in a sans-IO pattern: define your core, the interfaces, and your own types, (even if it seems redundant) and never, ever import a single dependency from a cloud provider in that core. Make two implementations of the interfaces: one in-memory that can be spun up quickly for testing and one that uses the actual cloud provider APIs. Now instead of hoping fakecloud or localstack update their mocks to be inline with AWS, all you have to do is update your dependencies and the implementation code and the core can be left alone for a long time.

This is also why I avoid lambda and other "serverless" compute like the plague because it's designed from the ground up to lock you in.