Hello again, how is life? Did you manage to demystify arrays yet? If you haven't you will want to work on simpler projects until they are second nature. A tile based platformer uses arrays or at least array concepts. The tile map itself is pretty much a big two dimensional array.
I feel like the #2 in the thread title is you blaming us the community. Blaming us for not giving you exactly what you want in the way you expect it. Suddenly it is now our fault if you don't succeed instead of your own. That being said, I want you to succeed. You are free to ask as many questions as it takes, and it makes me glad to hear that you tried out sphitrec.
One problem is a simple scene doesn't really simplify the code. You still need all the same code for a dozen tiles as you do for hundreds. Taking out something like scrolling will simplify things. If you want that, I have Find the Exit. In Find the exit, you can also draw a level as simple as you like by modifying some data statements at the end of the code.
You should expect that no matter how you do it, a platformer game will be hundreds of lines long. For the last paragraph, basically anything on the 8 or 16 bit game consoles largely faked sloped tiles. You have either a formula (y = mx + b) or a lookup table (array of heights at a given pixel offset into the tile) that says how far down the character can fall or how much to adjust their y position while walking back and forth. Something like Angry Birds will instead use a physics engine like box2d, and I think everything was per pixel collisions on worms. All that said I heavily suggest that you will want to keep things as simple as you can for now. Add that stuff in after you have a simple version working.
In fact you might want to simplify things even more and try a 2D top down maze game where the player moves a full tile each time they move. That should make bgget dead simple.
Since I seem to make things too complicated, perhaps this link will help. https://jonathanwhiting.com/tutorial/collision/. The code is in Javascript but as long as you get the concepts I think it should help.