By no means an expert, but yes, as you said basically the top dozen or so teams from the top European leagues are breaking away from UEFA to form a super league. It's long been talked about but revenue pressures from COVID have pushed the top teams into making it a reality. Right now, in addition to their respective domestic leagues, the top Euro teams compete against each other in the UEFA Champions League, with the lower Europa League for teams who don't qualify for the Champions. Crucially, this new league would feature a permanent collection of teams that would not be subject to qualification or relegation. As it stands now, teams have to qualify for the Champions League. From a revenue perspective, the largest teams want something more predictable and less risky than the current arrangement in which they can be upset, eliminated early on points, or fail to qualify outright, which can be a huge $$$ hit. With all the biggest brands in Euro football in their own league, they'll be able to have a more predictable revenue stream and instantly become one of the most valuable TV contracts out there.
So who loses out? The UEFA, Europe's governing body of football, who operates the current Champions/Europa league tournaments. This new league isn't intended to conflict with teams' respective national leagues (English Premier League, La Liga, Serie A, etc), but does directly compete with the UEFA's CL/EL. They are ****ed that they'll be losing the best teams, and thus lots of money, for their tournament. All the teams not invited to the league are also ****ed, because it's closed (save for a 5 team rotating play-in) and would chiefly benefit the permanent members. And I suppose fans of The Magic of Sports are mad, because the league reduces the possibility of fun Cinderella stories where an afterthought David topples one of Europe's Goliaths in a super high-stakes contest (though I'd imagine many more fans are happy they don't have to wait till the Champions League to watch Europe's best square off). So the UEFA, with FIFA's backing, is trying to threaten all the teams involved in the proposed league with a variety of sanctions including expulsion and potentially barring players from representing their national teams.
Unclear how it will all shake out but what is certain is the amount of money at stake guarantees it's going to be a very acrimonious fight.