Have you tried our NSCollectionViewControlMBS control in Xojo?
We got it new in 21.0 and improved it for 21.1 version, so please try it in the next days with the upcoming plugin version.
You can have a resizable grid of containers controls for macOS here. Great as it allows you to use it with a thousand items and containers are created on the fly when you scroll or resize the control. Since we use ContainerControl in Xojo, you can put whatever control you like on them. The example uses an ImageWell with a Label.
The layout is controlled by the NSCollectionViewLayoutMBS class. You can configure it with NSCollectionViewFlowLayoutMBS, the items will nicely flow within the available area. That allows you to set the spacing between items, item size and section sizes.
Please do not hesitate to contact us with questions.