Have you checked the database for references to the old URL and have you tried fixing this with search & replace? (wp cli command: https://developer.ww.wp.xz.cn/cli/commands/search-replace/)
Security plugins can be a good solution but if you do not wish to use these you should also look at hosting providers that already offer security features and security guarantees for your site.
I believe you need to edit Rank Math plugins settings at WordPress Dashboard > Rank Math SEO > Titles & Meta to get website name shown before page title. (Rank Math guide: https://rankmath.com/kb/titles-and-meta/#posts)
