Nature has a set of favicons included. In advanced settings you can switch to your own favicons. You can create your own favicon package (e.g. using realfavicongenerator.net), create a folder 'favicons' inside Joomla's 'images' folder and upload the files there (using (S)FTP). Probably you will need to adapt the paths inside site.webmanifest and browserconfig.xml files.