Google had a feature that allowed you to filter search results by reading level. Though no longer available, this shows that search engines can evaluate readability. Beyond as a possible direct SEO ranking factor, it matters for improving user engagement.
The best way to consider reading level is to really know your target audience. Do you write above or below them? Do top competitors use similar language as you?
Good writing is clear, expressing ideas through shorter sentences and simpler words whenever possible.
You can use Microsoft Word’s readability statistics to get a Flesch Reading Ease score. Try reaching 60+, or Plain English, unless you need more technical verbiage. There are many free online tools to use for this as well.
To help even further, segment content through more headers, paragraphs, lists, images, and call-to-actions.