Similar to that in the Schrodinger's cat thought experiment the cat remains in superposition unless observed by an observer, also in the double slit experiment an electron is passing through both the slits until we observe one of it. Therefore, does an observer make significance in the outcome of quantum events.
The answer is ultimately yes, but the definition of observer in quantum mechanics is counterintuitively far from its colloquial definition, which is typically taken as "some conscious entity that does not interfere with a process." Instead, a quantum-mechanical observer is anything that interacts with a quantum system in such a way as to extract information from that system.
When you substitute the quantum-mechanical definition of observer in your statement, it reads: "Quantum systems are influenced by things that interact with them," which is now obviously true.