"blocks": {
			"core/button": {
				"typography": {
					"fontSizes": [
						{
							"name": "Button Medium",
							"slug": "button-medium",
							"size": "16px"
						},
						{
							"name": "Button Large",
							"slug": "button-large",
							"size": "23px"
						},
						{
							"name": "Button XLarge",
							"slug": "button-xlarge",
							"size": "42px"
						}
					]
				}
			}
		},

<div tabindex="0" class="block-editor-block-list__block wp-block has-button-xlarge-font-size is-selected wp-block-button" id="block-c564793c-672f-4b14-84be-ee439ea353ca" role="document" aria-label="Block: Button" data-block="c564793c-672f-4b14-84be-ee439ea353ca" data-type="core/button" data-title="Button">
    <div role="textbox" aria-multiline="true" aria-label="Button text" class="block-editor-rich-text__editable wp-block-button__link wp-element-button rich-text" contenteditable="true" style="white-space: pre-wrap; min-width: 1px;">Button 1</div>
</div>

<div class="wp-block-button has-custom-font-size has-button-xlarge-font-size">
    <a class="wp-block-button__link wp-element-button">Button 1</a>
</div>

.editor-styles-wrapper .wp-block-button .wp-block-button__link.has-button-xlarge-font-size {
    font-size: var(--wp--preset--font-size--button-xlarge) !important;
}

wp-block-button .wp-block-button__link.has-button-xlarge-font-size{font-size: var(--wp--preset--font-size--button-xlarge) !important;}