When vaccines work they are usually great at stopping the spread. For the original strain of covid, for example, it both stopped symptoms **and** stopped the spread.
The new variants however (such as delta, the most prevalent one, and omicron) it is either completely in effective or significantly less effective (hard to draw firm conclusions off what studies we have). The point is, its not effective at stopping the spread because the spike protein it encodes for is different in the variants and thus the antibodies are ineffective to a significant degree (if not completely).
yea masks im not sure about. The data in them are questionable in either direction so we can only speculate about how or if they are effective.
I think if you are very strict in how you use them they probably help, but most people, almost no one, handles mask with the level of rigor needed for them to be effective.
Its like saying "condoms are proven to work"... well yea, but not when you reuse them a dozen times and take them half-off half a dozen times during sex.