ConditionalRenderingOfListViewCommandSet.ts

@override
public onListViewUpdated(event: IListViewCommandSetListViewUpdatedParameters): void {
  const commandOne: Command = this.tryGetCommand('COMMAND_ONE');
  const commandTwo: Command = this.tryGetCommand('COMMAND_TWO);
  const commandThree: Command = this.tryGetCommand('COMMAND_THREE');

  // Hide commands by default
  commandOne.visible = false;
  commandTwo.visible = false;
  commandThree.visible = false;
  
  // See https://{tenant}.sharepoint.com/sites/{siteName}/_api/web/lists(guid'{listId}')/Fields
  // for list of fields that can be used for filtering

  if (event.selectedRows.length === 1) {

    const selectedRow = event.selectedRows[0];

    // Command One should only be visible if ListField is empty
    if (selectedRow.getValueByName("ListField") === "") {
      commandOne.visible = true;
    }

    // Command Two and Command Three should visible if ListField have a value
    if (selectedRow.getValueByName("ListField") !== "") {
      commandTwo.visible = true;
      commandThree.visible = true;
    }

    // Hide all commands if the item is a folder
    if (selectedRow.getValueByName("ContentType") === "Folder") {
      commandOne.visible = false;
      commandTwo.visible = false;
      commandThree.visible = false;
    }
  }
}