Add only 1 header, combine all header to 1 and seperate each preload source with comma
RewriteCond %{HTTP_COOKIE} !ls_smartpush [NC]
RewriteRule ^.*$ - [ENV=PRELOAD:true]
Header add Link "</wp-content/plugins/elementor/assets/lib/font-awesome/webfonts/fa-brands-400.woff2>; rel=preload;as=font;crossorigin=anonymous,</wp-content/uploads/sgf-css/mem8YaGs126MiZpBA-UFVZ0bf8pkAg.woff2>; rel=preload;as=font;crossorigin=anonymous" env=PRELOAD
Notice:
1.) This way to preload static sources in .htaccess will only work if filename will not be changed.
2.) Preload by using server PUSH must be enabled. You can verify it if you check if ls_smartpush cookie is set by LSWS.
3.) Apple Safari browser doesn’t support this way to preload. That’s why LSWS doesn’t set ls_smartpush cookie if user agent is Apple Safari device related.