Don't use fluid layout value in typography calculation.

src/wp-includes/block-supports/typography.php

@@ -517,7 +517,7 @@
 		: array();
 
 	// Defaults.
-	$default_maximum_viewport_width       = isset( $layout_settings['wideSize'] ) ? $layout_settings['wideSize'] : '1600px';
+	$default_maximum_viewport_width       = isset( $layout_settings['wideSize'] ) && ! empty( wp_get_typography_value_and_unit( $layout_settings['wideSize'] ) )  ? $layout_settings['wideSize'] : '1600px';
 	$default_minimum_viewport_width       = '320px';
 	$default_minimum_font_size_factor_max = 0.75;
 	$default_minimum_font_size_factor_min = 0.25;

tests/phpunit/data/themedir1/block-theme-child-with-fluid-layout/style.css

@@ -0,0 +1,8 @@
+/*
+Theme Name: Block Theme Child Theme With Fluid Layout
+Theme URI: https://wordpress.org/
+Description: For testing purposes only.
+Template: block-theme
+Version: 1.0.0
+Text Domain: block-theme-child-with-fluid-layout
+*/

tests/phpunit/data/themedir1/block-theme-child-with-fluid-layout/theme.json

@@ -0,0 +1,12 @@
+{
+	"version": 2,
+	"settings": {
+		"appearanceTools": true,
+		"layout": {
+			"wideSize": "clamp(1000px, 85vw, 2000px)"
+		},
+		"typography": {
+			"fluid": true
+		}
+	}
+}

tests/phpunit/tests/block-supports/typography.php

@@ -699,6 +699,11 @@ public function data_generate_block_supports_font_size_fixtures() {
 				'theme_slug'      => 'block-theme-child-with-fluid-typography-config',
 				'expected_output' => 'font-size:15px;',
 			),
+			'returns clamp value using default config if layout is fluid' => array(
+				'font_size_value' => '15px',
+				'theme_slug'      => 'block-theme-child-with-fluid-layout',
+				'expected_output' => 'font-size:clamp(14px, 0.875rem + ((1vw - 3.2px) * 0.078), 15px);',
+			),
 		);
 	}