A question about SEO text and the rules that matter

Hi,

I was wondering what the rules are in 2021 for writing texts in SEO and the amount of text about a certain topic. How much should you repeat yourself? How does Google punish you if you write too much of the same thing?

For example:

An e-commerce platform has 5 shopping categories. Each category has their own page with text. However on the frontpage they've chosen to write paragraphs about each category. The text is a short summary but not a copy-paste of the category pages. The text is accompanied by a h2 tag.

Is that good practice? To have small texts about each category all over the start page? Or should you just have a little generic paragraph about the whole site at the beginning?

Thanks in advance!