No, smart swimsuits are almost not transparent owing to the density of the fabric and the prints we choose.
However, the fabric is very thin due to the huge number of tiny pores that allow the sun’s rays to pass through and get you tanned. So, the level of transparency may depend on how much it is stretched on the body.
If you are very nervous and modest, then you should choose a more intense print that visually covers the body and creates an opaque effect. The more monochromatic the pattern, the more transparent it gets.