Set the noindex on the term, not globally. Rank Math's Titles & Meta → Categories setting hits every category archive at once. If you add categories later with different needs, you'd have to unwind it. The per-term setting is the same amount of work and doesn't commit you.
Keep Follow checked. Noindex + follow means the archive stays out of results while still passing equity to the posts listed on it. Noindex + nofollow would waste the internal linking, which is the one thing that page is genuinely good for.
WP Admin → Posts → Categories. Hover the "How Do I Tell" row and click Edit — the full edit screen, not Quick Edit. The URL will look like /wp-admin/term.php?taxonomy=category&tag_ID=….
On that screen, scroll past Name / Slug / Parent / Description. Below those fields, there's a Rank Math SEO metabox with tabs across the top (General, Advanced, sometimes Schema).
Open Advanced. You'll see Robots Meta with a toggle to enable custom settings. Switch it on, then check No Index and make sure Follow stays checked. Click Update.
If the Rank Math box isn't on that screen, it's usually one setting: go to Rank Math → Titles & Meta → Categories and confirm Add SEO Controls is toggled on for the taxonomy. That's what puts the metabox on term edit screens; with it off, there's nowhere to set anything per-category. Turn it on, then go back to the category.
Also worth a quick look while you're in Titles & Meta → Categories — check what the global default already is. Some setups ship with category archives noindexed sitewide, in which case you have nothing to do. If it's set to index there and you noindex the single term, the term setting wins.
Verify by loading /category/your-term-here/ and viewing the source. You want noindex, follow in the robots meta tag.