I have a reasonable lay level of understanding about why a vaccine that only causes your body to reproduce part of the vaccine trains your body to only respond to that part of the virus, which at best leave you susceptible to the inevitable variants, and can lead to antibody dependent enhancement which can lead to more severe disease when your immune system encounters similar viruses. MRNA vaccines can also lead to autoimmune disorders, where the cells producing the spike protein (your own cells), are identified as a threat by you immune sysyem, and it starts to attack those cells.
I could go into more detail, and describe more problems in more detail, but I'm just a backyard mechanic, internet warrior. So check out Vanden Bossche's video where he explains these problems with ADE, and vaccine induced selective pressure during outbreaks that drives the emergence of new variants. He may talk about shedding some, but, like I said, a lot of content out there, so I don't remember if he addresses shedding or not. Dr. Malone talks about the risks of mRNA vaccine use in humans, he might also discuss the shedding problem.