Uh, source? Media very much likes to simplify these things, but if you think of this in a probabilistic/continuous manner, rather than a "yes spread vs no spread" approach, the vaccines obviously reduce spread?
You're right that there's no definite answer to this, but the general consensus among doctors is that it doesn't prevent the virus from spreading.
OTOH, the measures that are being implemented for vaccinated vs. unvaccinated are out of proportion based on the evidence we have.
“ In a November press conference, Tedros Ghebreyesus, the director-general of the WHO, said that the vaccines were 60 percent protective against spreading the virus prior to the arrival of the delta variant. That number has dropped to 40 percent post-Delta. Omicron may worsen the problem, if, as suspected, it is more transmissible and leads to many more breakthrough infections.”