I forgot some details and have to learn sdl2 and plus OpenGL, but I could manage it. Problem is I dont have much time with uni and work :(

This isn't necessarily advice, but this is what I'd try making a game with the understanding that it's been a while and my first-draft code is probably going to suck. Then, at some point as the code-base got messier and messier to the point of hindering my progress and/or trouble-shooting (or at some point where I realized I really wanted a particular feature that would require a major overhaul) I'd start again from scratch. I wouldn't necessarily have made a game, but I would have, hopefully, used a lot of that information I hadn't used in a while and pushed myself a little farther.

That's just me...

As a PHP developer myself, many programming concepts stay fresh in my mind so applying them to game development comes more second nature. The bigger challenge is coming up with a project idea that interests you and realizing what kind of projects fall within your abilities. So you try to set your mind on something and apply it.

Trying one facet of game programming is one approach and usually simpler than making a whole game. I ported some A* pathfinding code and learned how it works and made a simple demo of it using HTML and Javascript. I saved the code and will probably come back to it later when I want to add pathfinding to an actual game I'm making.

I was thinking about creating two or more complicated 2d games like packman or tetris, RPG or sidescroller. Or all of them. And then advancing to OpenGL, because soon I will get Blue Book.

I agree on programming concepts, maybe I need to practice more gamedev concepts, I have Game Coding Complete and Game Engine Architecture books, maybe Its good for me to read them?

If I say start from scratch, are you pleased or disappointed? If I say pick up where you left off, are you pleased or disappointed?

Do whichever one makes you pleased :)

Tl ; DR
I took long break from gamedev but not programming in general.
So I am wondering if I need to recreate these simple games or I can start with more advanced concepts like AI, side scrolling, more physics etc.?

i've taken multiple breaks of multiple years in the 25 years i've been doing games. its just like riding a bike, you never forget. sure you get rusty, but you pick it up again pretty quick. just pick up again where you last left off, and you'll be back up to speed in no time.