Getting your favicon.ico to work with OctoberCMS
First, generate your icons. One great site to help you is:
https://realfavicongenerator.net
You'll get most of the instructions there.
However, the question arises - where to put the required files?
One approach is to put it in your assets folder and then adjust the meta link:
<link rel="icon" type="image/png" href="{{ 'assets/images/favicon.ico'|theme }}">
This is OK except many devices expect favicon.ico to be accessible from the website root.
So it's best to upload it straight to your public_html directory (or wherever your OctoberCMS root is. But then remember to adjust your .htaccess file! Specifically, allow access to the necessary files in the "White listed folders" part:
##
## White listed folders
##
RewriteCond %{REQUEST_FILENAME} -f
RewriteCond %{REQUEST_FILENAME} !/.well-known/*
RewriteCond %{REQUEST_FILENAME} !/storage/app/uploads/.*
RewriteCond %{REQUEST_FILENAME} !/storage/app/media/.*
RewriteCond %{REQUEST_FILENAME} !/storage/temp/public/.*
RewriteCond %{REQUEST_FILENAME} !/themes/.*/(assets|resources)/.*
RewriteCond %{REQUEST_FILENAME} !/plugins/.*/(assets|resources)/.*
RewriteCond %{REQUEST_FILENAME} !/modules/.*/(assets|resources)/.*
RewriteCond %{REQUEST_FILENAME} !/favicon.ico
RewriteCond %{REQUEST_FILENAME} !/android-chrome-192x192.png
RewriteCond %{REQUEST_FILENAME} !/android-chrome-256x256.png
RewriteCond %{REQUEST_FILENAME} !/apple-touch-icon.png
RewriteCond %{REQUEST_FILENAME} !/browserconfig.xml
RewriteCond %{REQUEST_FILENAME} !/favicon-16x16.png
RewriteCond %{REQUEST_FILENAME} !/favicon-32x32.png
RewriteCond %{REQUEST_FILENAME} !/mstile-150x150.png
RewriteCond %{REQUEST_FILENAME} !/safari-pinned-tab.svg
RewriteCond %{REQUEST_FILENAME} !/site.webmanifest
RewriteRule !^index.php index.php [L,NC]
```