What happens to other devices when I keep messages on one device for only 30 days?

Hello everyone.

The storage on my iPhone is full. Messages takes up 20GB of the storage. On my other Apple products I have a lot of storage.

What will happen to my messages, once I change the messages settings on the full iPhone from “keep messages: forever” to “keep messages: 30 days”?

Will the messages still be there on my other devices, for example my iPad?

Thanks in advance!