Confirmation on Downtime for disabling cloudwatch log exports

Disabling CloudWatch log exports will not cause any downtime or require a database reboot. Changes to CloudWatch log export configuration are always applied immediately to the DB instance, and this change does not cause any downtime. The apply immediately setting is ignored for this particular modification, meaning the change takes effect right away regardless of whether you select apply immediately or schedule it for the maintenance window. You can safely disable the Audit, Error, General, and Slow Query logs without impacting your database availability.
Sources
Settings for DB instances - Amazon Relational Database Service
modify_db_instance - Boto3 1.42.51 documentation
RDS for PostgreSQL database log files - Amazon Relational Database Service

While the AI-generated answer is correct regarding the downtime, there is an important detail to keep in mind regarding storage and parameters:

• CloudWatch Export vs. Local Logging: Disabling the CloudWatch export only stops shipping the logs to CloudWatch. If slow_query_log or general_log remain enabled in your custom DB Parameter Group, the database will continue to write these logs locally.

• Storage Consumption: Local logs consume space on your DB storage volume. If you want to stop logging entirely to save storage or I/O, make sure to disable the parameters in your Parameter Group as well (which are dynamic and also won't require a reboot).

Just clearing the checkboxes in the RDS modification wizard is completely safe and won't cause any downtime or reboot.