After getting introduced to your value proposition with a “hero section” at the top of the homepage, the next step is to help them decide where to go on your site (which category to open). A list of main categories serves that purpose.
I recommend putting it directly below the hero section, or at least high up on the homepage. The other section that I usually recommend right below the hero section is social proof or credibility components.
One of things that I find interesting about IKEA’s site is that they feature 3 categories right below the fold.
Then have a section “Shop by Category” lower on the homepage.
The 3 featured categories are the equivalent to a link bar on mobile. Normally I recommend to have something like their “Shop by Category” section right below the fold, but I like how they’ve featured 3 to start with and have a longer list later on.