There is an oh-repeater widget type that you can define a widget that gets repeated in a loop. For example, you can look over members of a Group and create one row for each member of the Group. I know you can look over an index of numbers: OH3 MainUI oh-repeater "loop" value question. You can loop through Items with a given set of metadata: Question on fetchMetaData in oh-repeater. You can define the list in the widget properties: Widgets: add oh-repeater, dayjs to expression context by ghys · Pull Request #581 · openhab/openhab-webui · GitHub. But you would probably want to use the itemsWithTags (see previous link).
To show only those Items that are ON you can use an expression in the visibility property of the widget (see [Wiki] Building Pages in OH 3 - Item Customization on Auto Generated Pages) so it only shows when it’s ON.
But if you want a summary of the number of ON alarms you’ll need to use a Group or a really long expression.