Programming is hard and takes a long time to learn, especially something like C++ combined with Unreal’s extra stuff. You have to do it a lot before you start doing things without thinking about it and even then you’ll still be looking things up all the time when it comes to more niche tasks that you don’t do all the time.
Even starting with an easier language like C#.NET, it took me years to get really comfortable with it. I’d say the main thing is not to expect to ever know everything off by heart. You just want to be able to look something up and understand it and implement it relatively easily reading the documentation or seeing examples etc. I’ve made a living off software development for several years and I still have to google things all the time. There’s plenty of memes about how much professional developers use google and stackoverflow etc.
Having said that, some things that helped me learn:
Make it a habit to type things out yourself instead of just copying and pasting from tutorials etc. Even if you think you’re reading through it and understanding it, its surprising how little you take in when you just copy/paste. Then when you hit a problem and google it, make sure you’re understanding WHY the solution works and yours didn’t. That will require more googling and maybe even asking on here, but its much better than just copying/pasting and not really learning anything.
Oh also there was a good video from GMTK recently that covers something similar to what you’re saying: How I learned Unity without following tutorials - YouTube