The library we are using for post formatting has a scheme whitelist feature. By default, only http:// and https:// are allowed.
This feature is documented here https://s9etextformatter.readthedocs.io/Filters/URL_features/Schemes/
You could whitelist additional schemes via your extend.php file with something like this:
<?php
use Flarum\Extend;
return [
(new Extend\Formatter())->configure(function ($configurator) {
$configurator->urlConfig->allowScheme('magnet');
}),
];
Don't forget to clear Flarum's cache for the new formatter configuration to apply.
