I want to make a managerial app for Android, in which clients send their report to their manager. These reports are text and need to be saved on a cloud sql server. Is there any free SQL Server with limited storage but unlimited time period?
Nothing in the cloud is free, the best you can do is a free trial or student/developer subscription, but the latter tends to have limits or restrictions on their use (non-commercial and/or non-production).
SQL Azure can be used for about $5 per month. You may be able to use SQL Server Express Edition (free for all use types) on an Azure VM for less than that. You could also run SQLite on a VM, or PostGreSQL.
Another VM option is to use Linux, it might be cheaper than a Windows VM. There are also other cloud providers like Digital Ocean and Linode that might be free or cheaper than Azure. You can run SQL Server 2017 and 2019 on Linux and in Docker containers, but I'm not sure if Express Edition is supported on those. Other SQL Server editions are paid, and Developer Edition can't be used in a production setting.