Would it also be correct to say the boxes are made "from" plastic?
Yes, right too. In Portuguese both are expressed the same way.
it told me it's wrong
Same here. 2021 May 4
Obrigada, Paulenrique. :)
Should "Made out of plastic" also work? I almost always say "made out of" when referring to the material that something is composed of... it should mean the same thing. It gets marked wrong though.