Learning ROS2 without ROS1 background

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It's possible, but with the current state of ROS 2 material / documentation I would probably suggest to get at least some experience with ROS 1.

You'll probably have a much easier time matching ROS 1 domain concepts with their analogues in ROS 2.

You will have to "unlearn" some things though (nodelets fi don't exist in ROS 2) but most of the times at least the concept is similar which allows you to employ conceptual reuse (the idea of nodelets can be mapped to ROS 2 nodes running in the same component and using zero-copy exchange of messages). That helps me personally tremendously.