Yes, even regular car seats are laced with harmful flame retardants and made with synthetic fabrics etc. too. This is why I was so excited to find Clek. Check out what they have to say about their high-back, convertible booster car seat:
“We design car seats that we use for our own kids. That's why we became the first car seat company to remove brominated and chlorinated flame retardants from our car seats in 2014. In 2018, we introduced the world's first convertible car seats and booster seats made without any added flame retardants, featuring ethically sourced 100% Merino wool.”