String Theory was originally an attempt to combine the Gravity of General Relativity and Quantum theory.

String Theory claims to have successfully reproduced all of General Relativity. So all 100 years of experimental evidence for General Relativity also supports String Theory.

Unfortunately, String Theory has not yet reproduced the Standard Model of Quantum Theory. So none of the 70+ years of experimental evidence for Quantum Theory can be used to support String Theory.

According to Occam's Razor, when faced with two competing theories with equal predictive power, choose the simpler one. At this point in time, the simpler one is not String Theory.

Similarly, when faced with two competing theories with equal predictive power (UFOs or a tangled string of meteorology balloons), choose the simpler one. At this point in time, the simpler one is not UFOs.