So far there is a serious shortage of scientific papers demonstrating harm from microplastics. This paper attempts to make such a demonstration, but it does so by using extremely high concentrations, far beyond what could be achieved naturally.

While the concentration of plastic used in these solutions was higher than what a baby would be exposed to by eating from a microwaved food jar in real life

This popsci article briefly touches on this, but if you read the research paper, they actually used concentrations that were orders of magnitude higher. So high, in fact, that cell death would also occur with many inert and safe substances at these concentrations.

It's very concerning that we're exposing ourselves to this stuff without fully understanding it. But alarmist papers like this are unproductive at best. At worst, they lead to alert fatigue in consumers, in the vein of "this product is known to the state of California to cause cancer."