There are several factors that can affect the speed of a WordPress website, and the theme is just one of them. Here are some tips for selecting a theme that can help improve the speed of your website:

Choose a lightweight theme: A lightweight theme will have fewer resources, such as images and JavaScript files, which can help improve the speed of your website.
Look for a theme that is optimized for performance: Some themes are specifically designed to be fast and efficient, so they can be a good choice if speed is a priority.
Avoid themes with lots of features and options: Themes with a lot of features and options can be appealing, but they can also add extra bloat to your website, which can slow it down.
Consider using a caching plugin: Caching can help improve the speed of your website by storing static versions of your pages and posts, so they can be served more quickly to visitors.

In addition to these tips, it’s also important to optimize the images on your website and use a good quality web hosting provider, as these can also have a big impact on the speed of your website