Based on the behavior shown in the screenshot, this appears to be expected behavior of the modern model-driven app grid rather than a bug or ribbon
customization issue.
When you apply a Group By operation (for example, Modified On (Year)), the grid switches from a standard record list to a grouped/aggregated view.
In this mode, records are displayed as expandable groups (e.g., 2023, 2024, 2025, 2026) rather than as a flat dataset.
Because of this, many commands that operate on individual records or a standard record set—such as Export to Excel, Bulk Edit, and some other command bar
actions—are not supported. As a result, the command bar may be hidden or significantly reduced when grouping is enabled.