Have scientists been able to isolate/identify the virus for COVID-19?
Yes. Chinese doctors, WHO, and CDC were able to sequence (identify the virus and completely document) the genetic code of what was then called 2019-NCoV (2019 Novel COronaVirus). As early as January 2020, we had peer-reviewed publications documenting the sequencing of 2019-NCoV (now called SARS-CoV-2 due to its similarities with the original SARS-CoV).
This sequencing involves the entire genome of the virus, which allows us to determine that it was indeed a novel virus, and it allowed us to identify the genetic code which translates into the major proteins of the virus.
The basis for the question about identification of the virus is actually a blatant attempt at spreading doubt and misinformation. The root of this question actually comes from a debunked theory from the 1800s which denied that infectious organisms cause diseases. The theory was touted by Béchamp, as a competitive theory to Pasteur’s Germ theory.
One of the most compelling examples of the error of Béchamp’s Terrain theory is that he claimed bacteria change from one bacteria type to another, depending on the environment (hence why it’s called the Terrain theory, referencing the terrain or environment). With the technology we have today, we can show that there are considerable genetic differences between types of bacteria, which disproves the theory that bacteria can drastically change their type based on the environment.
Béchamp’s theory is a major component to much of the pseudoscience beliefs about nutrition as medicine, alkaline water, etcetera as the individuals touting and buying these products believe they can change bacteria based on the environment (body) through diet.