Struggling to filter News from one site to another

You are on the right track, but this is not going to work. Columns are not shared across sites. You need to create the same site column on each site independently. They can share the same values from the same term set, but only the term set needs to be set up centrally, not the column. Set up the site column on the IT site (make sure it is a site, not a list column) then add that column to the site pages library on the IT site. Add some articles and make sure you have NewsTopic = Cybersecurity associated to those articles and make you publish the articles. You will need to wait for the search index to run, but once it has, you can go back to the main home page and select the source for the News web part to be the IT site and then choose managed property as the filter. Page properties do not work when you are choosing a source from another site. You can then search for NewsTopic and your filter should use contains Cybersecurity and then it should work.  (You won't see NewsTopic exactly - you will see something like owstaxidNewsTopic.)