To accomplish this, you can add a section to a page, for example on my homepage, I was able to "Add a Section." Once I added a section, I used the newsletter block. I filled out the necessary information and saved the newsletter. Then, I clicked on the Page Settings of that section. Then click on General. Scroll until you see "url slug" and make sure you change it to sign up, newsletter, or membership (whatever you want). Then, your new url should look like, "www.yourwebsite.com/urlslug"
Whenever you use that url, only the newsletter section will be displayed, but the website menu will still show at the top. I was able to add this link to my Linktree and other places. Very convenient.
This worked for my website. Check it out: www.DunnitFilms.com/membership
I also use the promotional pop up feature to encourage people to sign up when they first come to the site.
Hope this helps!