Mark Jaquith

This simple plugin (no configuration) redirects <code>?s=FOO</code> search URLs to the nicer <code>/search/FOO</code> versions. Requires pretty permalinks.

Nice Search

Redirects search URLs from ?s=FOO  to /search/foo and converts spaces to + symbols

Andrei Zhitkov

Defining your default canonical arbitrary is most useful for those unfortunate souls who have their site URLs in punycode. This plugin allows setting a default custom URL to be used as canonical. It is designed to work with Yoast SEO only. The individual settings are still available and can be edited as before. Since it is dependent on presence of Yoast SEO, this plugin will not activate without it. 
The plugin does not add its own settings page, It uses WordPress Settings -> General. Look for it at the bottom of that page.
<h3>Technical Details</h3>
Supported versions: 
WordPress 4.x 
WordPress 5.x 
WordPress 6.x 
Yoast SEO 6.x-20.x

Custom canonical URL for Yoast SEO

This plugin allows setting a default custom URL to be used as canonical. It is designed to work with Yoast SEO only.

Nice Search vs Custom canonical URL for Yoast SEO