Why is my iCloud deleted mail retained for only a week

I want iCloud mail to retain deleted messages for 30 days. Until recently, this is just how it behaved.

Now, deleted messages disappear after only one week.

I checked settings everywhere I access my mail: the mail app on my MacBook has it set to retain deleted messages for 30 days. There used to be a similar setting on my iPhone, but it seems to be gone in iOS 15. I also don't see such a setting on iCloud.com.

So my question is: why is my deleted mail getting deleted after only one week, and how do I stop this from happening?

Thanks!

Ken