Whenever we engineer a piece of DNA to produce a specific protein or RNA, we have to put signals into it so that the enzymes that make RNA know that there is a DNA sequence that they must copy. The SV40 promoter used in the plasmids encoding SARS-CoV-2 spike protein is one of those signals. It tells the RNA polymerases (then enzymes that make RNA) where to start making the spike mRNA. The SV40 promoter contains no genes, meaning that no part of it can be copied into RNA. In order for SV40 to act as an oncovirus, the whole virus must be present. It is not present during any part of the vaccine mRNA manufacturing process. Only the promoter is present, and that can be made without having any virus present.
Residual DNA contaminants of SV40 have been found in the Jim Jones Jab.
https://osf.io/preprints/osf/mjc97