There is no limit with capacity providers and using Fargate Spot with platform version 1.4, what you are seeing is instead that there is relatively little Spot capacity for platform version 1.4 at the moment as we have focused on platform version 1.3 capacity for Fargate Spot, driven by customer demand. You will see this change shortly and can expect increased Spot capacity for platform version 1.4.
Also, please do keep in mind that there is inherently no guarantee that Spot capacity will be available for any platform version. If you are running a service it would be appropriate to have a mix of Spot and on-demand capacity configured to ensure you can run tasks for the service.
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