The "List of categories" block contains a table with two columns: a category name and the number of courses in that category. There are no labels or column headings to help users understand what those columns represent.
Why it matters

Envisioning a table is much easier for sighted users than screen reader users.

Possible solution

The best solution would be to use a simple list, e.g.,

• 4 courses in "Beginner"
• 2 courses in "Prerequisites"

This needs no additional labels or explanations, maintains a column layout, and is easier to read.