Logic GP 2021

This weekend, the first round of the Logic GP will take place. Instructions are available on the competition website:
https://gp.worldpuzzle.org/content/instruction-booklet-2

You must register to participate. Each round has 90 minutes to complete. You must complete as many tasks as possible in this time.

The 2nd round of the Logic GP has begun.

Hello! In the 2nd round, the tasks included Yin-Yang (tasks 14-15). Can anyone share any tips on how to start this task? Especially the 15th one (105p), I managed to do the easier one myself, but I can't even begin to tackle the difficult one.
All thoughts welcome :)

Do you know what edge connection means?
And are you aware that there should never be a situation where a 2x2 square has 2 black and 2 white pieces so that the same colors are in opposite corners?

From here you can start explaining further depending on what your knowledge is.

I'll write them down just in case.
The 2x2 rule means that a situation like the one in the attached diagram cannot occur anywhere.

Let me explain:
One rule of the task is that all circles of the same color must be connected to each other along their edges.
If, for example, the black circles in the example diagram were connected, one white circle would remain isolated. However, this is against the rules.

Edge connection:
A situation like the one in the top left corner should not occur.
For example, if you connect black circles together, the white circle between the two black ones will remain isolated.

In the situation below, it is certain that the area between the two whites must be filled with white circles, because black cannot be there (black would remain isolated). And this is called edge connection, because you can connect these colors along the edge.

For this particular task, there is an additional rule that all areas must have an equal number of black and white circles. This is a very important rule.

I colored 2 shapes blue. These are shapes where the squares along the edge are more than 1/2 of the total number of squares in the shape. The leftmost shape is 8 squares, but 5 squares touch the edge.
The rightmost shape is 10 squares in size, but 6 squares touch the edge.

This means that in both shapes, the shape touching the edge cannot have only circles of one color.

This is where edge connection comes in. Since circles of the same color must be connected along the edge, and considering that these shapes cannot have all circles of the same color on the edge, it is known that white circles must be drawn on the bottom right edge and black circles must be drawn on the top right edge.

So, you can solve as many as shown below.

And it should be a little easier from here on out.

Hello!

If I were to try to summarize my thoughts, I would have to say that I figured out bits and pieces of each rule, but I didn't get to the bigger picture, or maybe I didn't generalize the ideas enough. All the ideas you wrote down are understandable and extremely logical. I will definitely try to solve this again with a fresh perspective.
I have to say that this year there seem to be quite a few tasks that are a bit more abstract for me (SPOLICY, Pentominous, Yin-Yang, Shape Placement). I would also classify Hungarian Numberlink there, but I was able to find solutions faster, not too quickly. It seems that I am better able to solve tasks related to numbers or those where some simpler rule immediately stands out. Probably it is a matter of little experience with such (named) tasks.
Thanks a lot for the tips, TiiT!

Round 3 starts on Friday. So try not to sleep in :)
Instructions here: https://gp.worldpuzzle.org/content/instruction-booklet-2

Germany and Bulgaria are collaborating this time.
It seems like there are a lot of so-called classic tasks this time. So it's definitely worth a try for everyone.