help me decide

In short: Codeigniter is fast and easy to learn. And it has a lot of nice people here at the forum.

I've read (almost everywhere) that CI 3 is easy to learn. Does this apply to CI 4 as well?

I am not the right person to answer that since I've only touched CI4 briefly. But, if it's your first framework, I think it is better to start with ci3, since there are many more tutorials out there. When you've learned ci3 you can stick to that or move along to ci4.

Have fun!