Can I use non-wordpress themes in Wordpress on my hosted server? Just want to know whether themes that were not made for or by WORDPRESS will work in Wordpress?
WordPress can't use themes designed for other platforms (for instance, you can't use Ghost CMS themes in WordPress because they weren't designed for the platform).
To answer the second part of your question, you can use any third-party theme made for WordPress even if it was not made by the WordPress development team. The most popular themes for WordPress are often made by third-party developers. You can find thousands of free third-party themes listed on https://wordpress.org/themes/, including some of the most popular ones like Astra, Kadence, and GeneratePress.
You can also find paid third-party themes on other sites, however for most people, a good free theme like some of the ones I mentioned above will offer enough features to sufficiently customize your website.