What is the ruling on a Muslim consuming food products made for vegetarians from mushroom derivatives, such as meat substitutes? And is plant-based pork halal?

There is no harm in using products made from the meat of sheep, cattle, chicken, and the like, provided they are ritually slaughtered (dhakāt), and no forbidden substances were used in their processing. As for "vegetarian pork," anything made from pork or to which any of its fat, meat, or blood has been added is unlawful, unless the manufacturing process has transformed it to the point of complete istihalah (total chemical transformation).