I only disagree with the Modern Church if and only if it is in contradiction with prior Church teaching
Sedevacantism is actually a nuanced position if you can believe it or not
If one were to look at literally every single historical western institution they would notice it is in a similar condition to the catholic church
I would say this is caused by a grand conspiracy in relation to the end times
You don't have to believe that, but i do, which is why I believe in Sedevacantism.