When working with branch versioned data, if edits are performed directly on the Default version of the geodatabase, the Save and Discard edit buttons are disabled by default. This is because edits made on the Default version cannot be undone.
Both buttons remain disabled even if the option to automatically save edits is not enabled.
As the Default version is the ancestor of every other version in a geodatabase, and usually represents the published version, it is essential to protect it by setting the access level to Protected. This will prevent accidental alterations or corruption of the Default version. Refer to ArcGIS Pro: Protect the default version for more information.