Is it OK for SEO to also use the page title as the meta description?

The page title represents the subject of the content of each separate web page. The meta description provides a short and meaningful description of the content of each separate web page.

Check out the following Google guidelines for metadata:

Page titles should be descriptive and concise. Avoid vague descriptors like "Home" for your home page, or "Profile" for a specific person's profile.

Avoid keyword stuffing.

Avoid repeated or boilerplate titles. It’s important to have distinct, descriptive titles for each page on your site.

Why the search result title might differ from the page's tag

If we’ve detected that a particular result has one of the above issues with its title, we may try to generate an improved title from anchors, on-page text, or other sources.

Create good meta descriptions Google will sometimes use the description tag from a page to generate a search results snippet, if we think it gives users a more accurate description than would be possible purely from the on-page content. A meta description tag should generally inform and interest users with a short, relevant summary of what a particular page is about. They are like a pitch that convince the user that the page is exactly what they're looking for.

Include clearly tagged facts in the description. The meta description doesn't just have to be in sentence format; it's also a great place to include information about the page.

Use quality descriptions. Finally, make sure your descriptions are

truly descriptive. Because the meta descriptions aren't displayed in the pages the user sees, it's easy to let this content slide. But high-quality descriptions can be displayed in Google's search results, and can go a long way to improving the quality and quantity of your search traffic.

I recommend that you do not use duplicate content anywhere on your website, including metadata.