A study looked at 43 different plastic products, including four petroleum-based.

"Most bioplastics and plant-based materials contain toxic chemicals.
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Cellulose and starch-based products induce the strongest in vitro toxicity.
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Most samples contain >1000 chemical features; the maximum is 20,000 features.
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The material type does not predict toxicity or chemical composition.
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Bio-based/biodegradable materials and conventional plastics are similarly toxic."

Are bioplastics and plant-based materials safer than conventional plastics? In vitro toxicity and chemical composition
https://www.sciencedirect.com/science/article/pii/S0160412020320213

from Vera Salt:
"We’re proud to use packaging that’s 100% plastic-free. The inner bag, which can look like plastic, is actually made from potato starch, as noted on the side of the box. It’s biodegradable, compostable, and a sustainable alternative to traditional plastics."

Note that they don't claim their bags are less toxic, nor safer than traditional plastic.

Potato starch is non-toxic, but it looks like in order to make starch into a plastic they have to use plasticizers, which ARE toxic. So unless Vera Salt has some method of producing non-toxic bioplastic, which they make no claim to, their bags are a gimmick, and their "microplastic free" salt isn't microplastic free by the time you receive it.