By the rules as written, a druid can take the form of "a beast that you have seen before." If the creature is still classified as a beast rather than a monstrosity and if the druid has seen it, then by the rules, yes.
— Keith Baker (@HellcowKeith) November 1, 2020
If the creature is classified as a beast, it's still LARGELY natural even if magebred. If you feel the magebreeding makes it fundamentally unnatural, then it should be classified as a monstrosity or aberration.
— Keith Baker (@HellcowKeith) November 1, 2020