RAW, objects can occupy spaces.
Many game features permit movement into, or appearance in, an unoccupied space, while forbidding them to occupied spaces. Unfortunately, what makes a space 'occupied' is never defined.
Typically a space is considered occupied when it has a creature controlling it, but creatures are not the only things that can occupy spaces; objects can as well.
We know this from the text of dimension door (emphasis mine):
If you would arrive in a place already occupied by an object or a creature, you and any creature traveling with you each take 4d6 force damage, and the spell fails to teleport you.
It is also apparent in the description of a figurine of wondrous power (emphases mine):
If the space where the creature would appear is occupied by other creatures or objects, or if there isn't enough space for the creature, the figurine doesn't become a creature.
RAI, larger objects occupy space - but we are not told how large they need to be to do so
In response to a question about whether a spiritual weapon denies use of a space to creatures, Jeremy Crawford wrote:
A spiritual weapon doesn't pass through walls. It also doesn't occupy its space; it's not a creature, and it's not described as being large enough to fill its space.
Now, a spiritual weapon is not an object, it is a spell effect - but we can take Crawford's general point that in order to occupy a space, a thing needs to be large enough to fill the space (or, like a creature, be actively controlling the space to deny entry).
However, what we are not told is how large is large enough. We might guess that it would take a Medium-sized object to fill a Medium space (5' x 5', the space controlled by a Medium creature). In the DMG's description of Objects we are given chests and lutes as examples of Small objects, and barrels and chandeliers as examples of Medium objects. A large and ornate chandelier, if for some reason on the floor, could easily prevent a creature from moving through the space. A barrel, which we can take to be the kind of barrel that is significantly larger than a chest and thus probably a hogshead or larger, might be difficult terrain and cover on the small end, or prevent movement through the space on the large end.
DMs decide what is difficult and what is impassable
Thus there is some line between objects making spaces harder to pass through (difficult terrain) and them being large enough to fill their space, denying entry. That line is for the DM to determine. The PHB gives guidance in terms of what might be considered difficult, but passable, terrain and many of the examples have to do with negotiating objects as obstacles (emphases mine):
Boulder-strewn caverns, briar-choked forests, treacherous staircases--the setting of a typical fight contains difficult terrain...Low furniture, rubble, undergrowth, steep stairs, snow, and shallow bogs are examples of difficult terrain.