I think nonliving creatures may be more specific versions of objects then, since I couldn’t find any reference of creatures not being considered objects (because who would even say that, it should be obvious if you use your brain), but it also means that if a spell or ability only allows you to target or create objects and has no specification in regards to creatures, undead and constructs are valid targets by RAW.
If you look up the definition for an Object, it specifies that it is “a nonliving, distinct thing” — such as a corpse.
However, the definition of Creature does not say it must be living. So, a corpse is both a creature and an object.
There are even creatures that have never been living — such as constructs — and thus are also objects.
I think nonliving creatures may be more specific versions of objects then, since I couldn’t find any reference of creatures not being considered objects (because who would even say that, it should be obvious if you use your brain), but it also means that if a spell or ability only allows you to target or create objects and has no specification in regards to creatures, undead and constructs are valid targets by RAW.