Then you need to think critically about how that ability works. You have the knowledge to understand it. You just have to stop blindly complaining about anything that is true damage and evaluate what the mechanics are actually doing.
edit: To be more direct I'll make an example to show why it's not like other true damage. Let's say Zoe has 500 AP so the cap of Sleepy Trouble Bubble is 420. Let's say an equally damaging ability hits you for 420 but you have 100 MR so you take 210. That means the true damage will be 210 so you take a total of 420. If you look at it another way, what if it was implemented without true damage and instead it doubles the damage, still with the cap. Then you will take 840 halved by MR to 420. Either way it's 420.
The only reason they made it true damage was so that it would display the bonus damage separately. It is functionally identical to "double damage, with a cap" lol