Can I rank a particular page for more than one keyword if Yoast SEO only allows one keyword focus per page?

Yes, it's perfectly possible to rank for more than one keyword on a page. In fact, there isn't a set limit of keywords a page can rank for in Google search results. If a page is long enough and contains enough natural instances of a keyword, you can rank for it. The number of keywords you're trying to rank for won't affect your rankings negatively as long as you're not simply stuffing them in your content.

Rank for Many Long-tail Keywords

Even if you're not actively targeting certain keywords and only going after one or two short-tail keywords of about three words, you have the possibility of ranking for many more if your content includes a wide range of long-tail keywords that include those shorter terms. For instance, if you are targeting "bench press equipment" to rank for a blog post, you may rank for other longer terms that people search for such as "where can I buy bench press equipment" which you might include in a subheading.

While Yoast SEO might only allow for one focus keyword, you don't have to limit your keyword targets. There are plenty of analytics and reporting tools to help you see how well your page ranks for an infinite number of terms. Simply consider the Yoast SEO focus keyword as a basic indicator for a general topic keyword.