But The “Solution” Is Incomplete
Yes, dark matter exists and is the dominant form of matter in the cosmos. However, physicists do not know what it is, and cannot even make specific predictions about the dark matter. For decades they told us that the DM was “WIMPs”, or axions or sterile neutrinos, or some other hypothetical particle of unspecified mass, etc. Hundreds of experiments looking for them have come up empty. Meanwhile, the number of MACHOs and black holes and rogue planet-mass objects has grown astronomically (sorry could not resist). Do physicists now acknowledge that primordial astrophysical stellar-mass black holes have become a leading candidate for the dark matter. Oh no, that would be off-topic for their just-so story.
The evidence for large-scale cosmological acceleration is reasonably good, but the idea that we understand the “Dark Energy” phenomena is not correct. There are several different explanations for the observed cosmological acceleration. For example (1) the empirical evidence may be flawed and/or massaged to give the “correct” answer. (2) various inhomogeneous models can explain the acceleration without “DE” using only General Relativity. (3) Another non-”DE” explanation for the observed acceleration has been presented by three mathematicians, as linked below.
Bottom Line: Yes we have good evidence for Dark Matter, and fairly good evidence for large-scale cosmological acceleration. However, the enigmas of these phenomena have not been solved. We would do well to be open-minded as we work away from just-so stories and towards a real understanding of the cosmos.