WordPress | How to attach a thumbnail to a category without a plugin?

Question

PHP

We need a way to attach a thumbnail to a category without a plugin (When editing a category - insert a picture)
For the subsequent display of a list of categories with pictures and descriptions.
I know the descriptions, but there are problems with the pictures. Help me please.

Answer 1

What's wrong with the plugin?
By and large, the same code, but in a different file.