For a site with /en/... and /ar/... URLs, every page must declare all of its language versions — including itself — plus an x-default:
<link rel="alternate" hreflang="en" href="https://example.com/en/services">
<link rel="alternate" hreflang="ar" href="https://example.com/ar/services">
<link rel="alternate" hreflang="x-default" href="https://example.com/en/services">The two most common mistakes: pointing alternates at the homepage instead of the equivalent page, and forgetting the self-referencing tag. Both make Google ignore the whole set. Add the same alternates to your sitemap with xhtml:link entries for faster pickup.