Can you run the catalog on a NAS? Yes, you can. Does Lightroom (or Adobe) support this? No. The primary reason is likely because the Lightroom database can't be accessed from two different machines at the same time. There are temp files and other items in transit that the application depends on that would likely get corrupted if another machine attempted to access the LR database while it was open on another machine.

So, you could run it on a NAS, but unless you are extremely careful, and never, ever, ever open the database from your laptop while it is open on your iMac, then it might not be worth it.

I would suggest the following: Lightroom has a feature called 'Export as catalog' that helps you do sort of what you are looking to do:

In this case, you take the entire catalog, or perhaps the latest portion you are actively working on, and select those images, then 'Export as Catalog'. Be sure to include the images. This will copy all the edits and the images to a new catalog, that you will then move to your laptop.

Now you have a second copy of the catalog on the laptop. No, it is not synched, but synching is what would corrupt the catalog if you tried this via a NAS. Instead, you make your edits, and then you would import them back into your main LR catalog using 'Export as catalog' again (you don't need to include the images unless you have added new images to the laptop only), and import the changes back into the iMac/NAS.

You could also do a variation of this: "Export as Catalog" from the main computer. Do not include the images. Instead, when you load the catalog on the Macbook, 'find' the images on your connected NAS via the laptop, this will connect the exported catalog to the original image files on the NAS. NOTE: any changes on the laptop DO NOT change the images on the NAS, it only changes the data within the exported catalog, now on the laptop.

Once you make some edits, then you can export those edits using 'Export as Catalog', and import this file on the iMac, which will add all those laptop edits to the main iMac catalog. Using this method will also allow you to take advantage of 'Smart Previews', allowing you to keep a preview on the laptop for editing, without actually having all the images available.