Plastics might not be the only factor, I believe a lot of it has to do with lifestyle of average americans as well (obesity, sedentary, high sugar and fat diets) though I do think that plastics play a part as well.
He says early pregnancy failures have increased ten percent. The graph he links shows no such increase according to line of best fit. It only shows it if he cherry picks the largest observation in the data.
Even if I grant this false assumption, his inference that late miscarriages have declined doesn't even follow, the data he's presented is fully consistent with an increase in late miscarriage of a few percent.
Regarding the testosterone question. The data in the tweet you mention actually does show such a decline - of almost 50 percent in young US males. His point is that the decline has stopped and levels have increased by an extremely small amount in the last 10 years, although that could easily be statistical noise since it is such a tiny increase. Overall, his data shows a large decrease over 50-100 years in the US.
Plastics might not be the only factor, I believe a lot of it has to do with lifestyle of average americans as well (obesity, sedentary, high sugar and fat diets) though I do think that plastics play a part as well.