RDS Aurora MySQL with Auto Minor Upgrade is disabled

Yes, AWS can automatically upgrade your RDS Aurora MySQL database even if you have Auto Minor Version Upgrade disabled in certain circumstances.

This typically happens when your database is running a minor engine version that is approaching or has reached its end of standard support date. In these cases, AWS will perform automatic upgrades during your scheduled maintenance window to ensure your database remains on a supported version.

Before beginning these automatic upgrades, AWS sends an RDS operational notification through the Personal Health Dashboard (PHD) approximately 3 months in advance to inform you of the upcoming changes.

If you want to maintain greater control over when version upgrades occur, especially for production environments, you might consider using Aurora MySQL Long-Term Support (LTS) versions. These versions allow your DB clusters to remain on the same minor version for a longer period (at least three years or until the end of standard support for the major version).

For LTS versions specifically, it's recommended to disable automatic minor version upgrades to prevent your cluster from being upgraded to a non-LTS version. However, even with LTS versions, AWS may still perform automatic upgrades when the version is no longer supported.

If you have critical business requirements that necessitate control over upgrade timing, you may want to proactively upgrade your MySQL instance before any enforced upgrade window begins.
Sources
RDS database upgraded and restarted automatically despite having Auto Minor Version Upgrade disabled. | AWS re:Post
RDS database upgraded and restart despite having Auto Minor Version Upgrade disabled? | AWS re:Post
Would MySQL auto minor version upgrade be triggered in April? | AWS re:Post
Long-term support (LTS) and beta releases for Amazon Aurora MySQL - Amazon Aurora