010101 you need to use the view extender, that method of registering views will break extensions loaded after it...
(new Extend\View())->namespace('flarum-feeds', __DIR__.'/views'),
I'd also remove the
Compat closure, as that's deprecated. Try and use the
Extend\Event() extender if possible.
app()->url() is no longer supported, you'll need to make
Paths::class or inject via the constructor
https://github.com/zerosonesfun/flarum-ext-syndication/blob/8935db8acbb6a25318436dc4e60dd03fec8446eb/src/Listener/AddFeedsRoutes.php#L51 - think
ConfigureForumRoutes is also removed, but can't remember off the top of my head
array_get is removed, use
Arr::get in it's place
Some of the namespaces are not autoloaded, which will also be causing some issues too
Quite a few other small bits and pieces overall that simply are not gonna work on beta 15. There may be no Mithril to worry about, but the jump from Laravel 5.X to 6, along with the extender changes really do mean this extension needs quite the refactor, in my view...