To add a Link to a Button, you can follow these.
#1. Header Button
First, edit any pages on your site.
Next, hover on Header > Click Edit Site Header
Left click on Button > Click Link icon or Pen icon
and you can add URL, then wait 3-5 seconds, link will be saved automatically
#2. Button Block
You can click on Button Block and click Pen icon.
Next, click Attach Link
and you can enter Link.