Is there a way to create global content types? I can create a content type on my websitecollection and it is also available and usable in the subsites. However, I want to create a general content type that can be selected on every website collection.
Content Type Hub is a central location where you can manage and publish your content types. So now web applications can subscribe to this hub and pull down the published content types from the hub. Below is the reference link https://collab365.community/understanding-content-type-hub-cth-in-sharepoint-2013/
Just like other replies said, you will need to first create a site collection to function as a content type hub. Create all required global content type there, publish these content types. Then go to the site collections you wan to apply them.
Here is a quite detailed step-by-step tutorial, you can take it as an reference:https://www.spguides.com/content-type-hub-in-sharepoint/