The following is a list of resources for learning, staying up to date with, and using Xamarin.
Awesome Xamarin Forms is a curated list on GitHub of a bunch of resources for Xamarin. This includes controls, effects, behaviors, tools, and more. It's a good 'one-stop-shop' for everything Xamarin. https://github.com/jsuarezruiz/awesome-xamarin-forms.
Weekly Xamarin is a weekly newsletter sent every Friday or Saturday. It's a community-curated list of all the latest Xamarin news, blog posts, and podcasts. http://weeklyxamarin.com.
The best video courses for learning Xamarin are Asfend Yar Hamid's real-world app series on Udemy: https://www.udemy.com/user/asfendyar/
The best book for learning Xamarin is Xamarin.Forms Projects by Daniel Hindrikes and Johan Karlsson: https://www.packtpub.com/product/xamarin-forms-projects-second-edition/9781839210051.
SSW hosts a Xamarin Hack Day every year: https://xamarinhackday.com.
Xamarin has a thriving and passionate community and ecosystem. Many Xamarin developers have made awesome controls available either as open-source libraries, NuGet packages, or both. A lot of these can be found at the Awesome Xamarin GitHub page linked above. Additionally, a number of commercial options are available.
Xamarin Community Toolkit: This is a community-driven set of controls, effects, behaviors, and extensions that make add a lot of functionality you are likely to reuse in your projects. https://github.com/xamarin/XamarinCommunityToolkit.
SyncFusion: SyncFusion provides a set of beautiful controls and templates for a range of use cases and scenarios. There is also a community license, which allows you to use it free for anything earning less than $1m a year. https://www.syncfusion.com/xamarin-ui-controls.
Telerik: Progress has made their Telerik UI available for Xamarin.Forms. Telerik provides a range of controls focused on enterprise and business applications. https://www.telerik.com/xamarin-ui.
The best Xamarin stream is Kym Philpott's weekly stream on Twitch: https://www.twitch.tv/kymphillpotts.
There is a strong community of Xamarin streamers regularly producing awesome content. A curated list can be found here: https://aka.ms/xamstreamers.