have you scrubbed out the tray to remove grime and organic matter? And the inside of the fridge?
it would not be smelly unless blood or other materials were getting into it, as may happen if unwrapped food in the fridge contacts the back wall or drips into the collection gutter inside the cabinet.
After years of use, the tray will also collect dust, dead spiders etc and may get mouldy, but should need very little cleaning.
The tray is normally positioned on top of the motor so that waste heat will evaporate away clean water. If yours is filling up, the most likely explanation is that the door is not sealing tight enough, so humid air from the room is causing excessive condensation inside. It can also happen if you habitually put steaming bowls of soup, or a lot of washed salads, in the fridge, but this is uncommon.
p.s.
I see your fridge is an extra-cheap brand that was left behind by the previous occupant, so it is quite likely that age, wear, or poor quality have led to the door not sealing well