https://chrismenardtraining.com/post/remove-blank-page-inserting-envelope-word

If you’re like me, I cannot stand the extra page that is generated by Microsoft Word when you create an envelope to be printed. It wastes an perfectly fine piece of paper every time you want to print an envelope unless you hit print the first page only. Who does that? I don’t. I ended up using my Google-Fu and found this link above which shows you exactly how to get rid of the page. Make sure you save the file after you make the changes and delete the second page.