With Full Site Editing, I used the Query Loop Block – once per category – assigning it in each instance to display four columns, with one linked Featured Image per column. For a minimal appearance, I also removed the post title & date information. Other blocks were then added – spacer blocks, separator blocks – to format the page.
Next, I created several individual pages (one per portfolio project category), and returned each working link to my Full Portfolio page. As such, only four items per project category are displayed, with a link to see more.
WordPress Support was very helpful answering questions, and shared this instructional video regarding use of the Query Loop Block – thank you!