Can sertraline be used temporarily for venlafaxine?

That's something a doctor or pharmacist must answer.

I would not do that because it can take time for Venlafaxine to exit your system depending on the dosage you were given. Ask your doctor for samples!

Hi, Clara!
Although both are antidepressants they are from different classes and work somewhat differently. Potentially, you could have some discontinuation symptoms from missing the venlafaxine.
Using the sertraline could take a week or two before you might begin to feel any effects.

Talk to your doctor and ask if they might by chance have some venlafaxine samples and get their advice.
In the long run substituting might be better than stopping the venlafaxine cold turkey.
Best regards and best of luck with this.
Wildcat