Using multiple webviews is a red flag for me.
If you're loading content from a remote source (over the web) then the amount of memory used to render that content. Reclaiming that memory can also be a challenge.
I'd start by avoiding using multiple webviews and just create one that you reuse across multiple pages as necessary. (You may need to remove and reassign the parent or create at a "shell" level depending on the structure of your app.)
If you need multiple webviews on a single XAML page I'd also see if you can change things to avoid that if possible.
Of course, first use the built-in diagnostic tools to determine if this is where you should be looking https://learn.microsoft.com/en-us/visualstudio/profiling/profiling-feature-tour?view=vs-2019
To manage the memory used by webviews, you should make sure you're removing content before destroying instances and make sure you're disposing of everything correctly.
You may also benefit from maintaining a collection of webview instances that you reuse so that you can avoid creating more than are necessary.
HOWEVER, I would change the content so that you don't need a webview to display it.
WebViews are very heavyweight controls and using them to display a small piece of formatted text is overkill.
If at all possible, as the content is being shipped with the app, I would first convert it into a format that is easier to work with and so doesn't need a WebView to be rendered.