How to…
Duplicate Feature Grid
In page edit mode, click on the hamburger menu (the three staggered horizontal lines).

From the block list (see image below), click the three vertical dots (not shown) to the right of the last feature grid.

You will see the pop-up menu below. Click on Duplicate (ignore the fact that Copy is selected in the screen shot), and a new Feature Block will be added to the list of Feature Grids, which will have the same content as the Feature Grid that you duplicated. Then go into the block editor on the right side of the screen to edit its component blocks.

Broken Link Checker
Note: Choices in addons for link checkers were very limited, and some of them had low ratings. This one seems to be the best that I could find, and it has some shortcomings.
Go into the Dashboard (admin section), scroll down to the bottom in the left sidebar, and you will see the Link Checker, click on it, and you will see the expanded choices. Click “Local (old)”.

You will see the following:

First, IGNORE “403 Forbidden” in the second column. These are working links that are actually ok (it seems that the link checker has some quirks). The “404”and “410” errors are the ones that we are concerned about. Hover over the link (“URL column), and you will see a number of options. Click on “Unlink”
Note that you can check to see whether the link is truly broken by clicking on the link in the first column. That will attempt to go the linked website or page. You should get an error stating that the link is indeed broken.