This is a core block and thus available by default in Gutenberg WordPress editor. No download required.
The WordPress Button Block adds a clickable button to your web page or post. It can be linked to an external URL or to internal page or post. Adding a button in the classic WordPress editor was not possible, but a breeze in Gutenberg.
Button Block Features
Block toolbar has options for alignment and basic formatting. Button blocks sidebar settings panel has options to set text color and background color. It even comes with a few premade styles which you can set with a click.
This is how the button looks by default on the frontend. This may look different depending on the theme you use.
Button block has 3 different styles.
Button block has options to set text color and background color in the sidebar panel.
Once added the block you can add the external URL or start searching for page/post title in the url input field.