This matches the Rollup Multiple Boards app exactly. From an item in a high-level board you create as many down-level boards you want. These are create from a monday template (in your case these are the projects). On the high-level board you have recipes to sum (or average, min, max) numbers, statuses, time tracker and timeline.
The top board in the picture is your master board where the action status is used to create detail (project) boards. One project board is shown below the master board and you can see that the data in the master board “output” columns (the ones in the red eclips) comes from the detail board. A change in the detail board (column change or add item) will be immediately reflected in the master board corresponding item. Unfortunately the battery like status summary is not available in the monday API (I am discussing that with the monday team) therefore the status summary shows as “3 of 20 (delayed)”. You can choose another status value and a percentage, like “75% (done)”. The output columns are just normal number / text columns and can be used in other automations.
The “Health” column in the master is a RAG-style column where you can define in your recipe on which amount of delayed (or stuck or something else) items in the detail boards you want to color RAG (Red Amber Green)
The forth item in the master board shows the summary of another detail (project) board which is not shown in this picture. There is no need for any mirror and/or connected board column. All relationships are stored and maintained within the app.
In the example shown you also see filtering in action. The second and third item in the master board are duplicates from the first item. Using the dropdown columns in both the master and the detail has the effect that the master shows the summary for only those items that has matching dropdown values. The filtering option will be an extension to Rollup Multiple Boards and release within the next few weeks. You can filter on dropdown values and people values (persons).
You can also create multiple levels, master-master-master-detail. You can try the app for free for a 10-day trial period. More info on Downloads Archive | Excellent Team