Based on the information provided, I found two relevant sources for discussing the sales of Dupixent in 2020. Dupixent is a medication for treating atopic dermatitis, asthma, and chronic rhinosinusitis with nasal polyps, which is jointly developed by Regeneron Pharmaceuticals and Sanofi.

According to the first source, a drug patent watch website [1], Dupixent is a blockbuster drug, which means it generates annual sales of more than $1 billion. However, it does not provide specific sales figures for 2020.

To find more detailed information, I consulted the second and third sources, which are the financial reports of Regeneron Pharmaceuticals [2] and Sanofi [3], respectively. Both companies reported the sales of Dupixent in their financial statements.

In Regeneron's fourth-quarter and full-year 2020 financial results [2], the company announced that Dupixent generated net product sales of $3.93 billion in 2020, representing a 75% increase from the previous year. Specifically, Dupixent's net sales in the fourth quarter of 2020 were $1.17 billion, up from $578 million in the same period of 2019.

Similarly, Sanofi's press release [3] reported that Dupixent achieved sales of €3.1 billion ($3.77 billion) in 2020, representing a 65% increase from the previous year. The sales of Dupixent in the fourth quarter of 2020 were €821 million ($998 million), up from €461 million ($564 million) in the same period of 2019.

Therefore, based on the information provided and my research, Dupixent's sales in 2020 were approximately $3.93 billion, according to Regeneron's financial report [2], or €3.1 billion ($3.77 billion), according to Sanofi's financial report [3].

References:
[1] <https://www.drugpatentwatch.com/p/biologics/tradename/DUPIXENT>
[2] <https://investor.regeneron.com/news-releases/news-release-details/regeneron-reports-fourth-quarter-and-full-year-2020-financial>
[3] <https://www.sanofi.com/en/media-room/press-releases/2021/2021-02-05-06-30-00-2170436>