Make sure you didn’t block JavaScript files by mistake
If Google cannot render your page properly, you should make sure you didn’t block important JavaScript files for Googlebot in robots.txt
TL;DR: What is robots.txt?
It’s a plain text file that instructs Googlebot or any other search engine bot if they are allowed to request a page/resource.
Fortunately, the URL Inspection tool points out all the resources of a rendered page that are blocked by robots.txt.
But how can you tell if a blocked resource is important from the rendering point of view?
You have two options: Basic and Advanced.
Basic
In most cases, it may be a good idea to simply ask your developers about it. They created your website, so they should know it well.
Obviously, if the name of a script is called content.js or productListing.js, it’s probably relevant and shouldn’t be blocked.
Unfortunately, as for now, URL Inspection doesn't inform you about the severity of a blocked JS file. The previous Google Fetch and Render had such an option:
