There are multiple ways, and it depends on where the button is going to be used. Your button examply is not really a button but a link, styled as button.
in a textarea field: use a link kirbytag and style as button on the frontend if really necessary: (link: …) | Kirby CMS
in a blocks/layout field: create a custom button block: Blocks | Kirby CMS
a structure field with a single item with one field for text and on for the link can be use for a stand-alone button
The link field plugins provides another way for a stand-alone button: Link Field | Kirby CMS
If you want to link to a page, a pages field could be used to select the page to link to (url and text would come from the selected page)