For example, https://www.dovepress.com/positive-predictive-value-of-the-i..., A Danish cohort of over 20k people that had a positive Covid test, 1.4% have subsequently been diagnosed with long Covid.
Now, you could continue to be really skeptical (are these really Covid related, or would these have happened absent Covid?). To say zero scientific evidence though seems to me to be sticking your head in the sand.