The game of football has never changed in terms of the basic rules of the game, but what is happening now is a change in the competition format held by UEFA and not the rules of the football game so we must to be able to differentiate between them, usually every change that occurs in a competition aims to make the competition better in future and I think there may be shortcomings that need to be improved from the old format, whether it is complicated or not to understand the new format of course it's just matter of time and there are not many changes that have occurred in the new format apart from adding participant slots, changing the group phase to the semi phase league and also several other regulations that perhaps we will understand after the first season of the UEFA League with the new format ends at the end of next season.
If you really want to understand more about the new UEFA competition format next season, of course there's no harm in reading the article below:
https://www.uefa.com/uefachampionsleague/news/0268-12157d69ce2d-9f011c70f6fa-1000--new-format-for-champions-league-post-2024-everything-you-ne/I think there are also changes in terms of the rules of the game, for example in the goalkeeper's position during a penalty, there is a change in the rules that are now a guideline for them. Although not as significant as the changes in the competition format, it is still a rule that has changed in the game. In the past, the handball rule, for example, any movement could constitute a handball violation as long as the hand touched the ball, but now we must first see whether the player's hand is active or not so that it can be called a handball, not to mention that it is greatly helped by the presence of VAR. Talking about the new format of the Champions League and the European League which will be implemented for the first time, as you said for some people it takes longer to really understand it, but over time I think it will be easier to understand, especially since we will also see the practice directly.