This should not come as a surprise, and it was largely predictable from the outset. The flu has a base reproduction number (R0) less than 2 ( https://www.vdh.virginia.gov/coronavirus/2020/12/07/covid-19... ). Covid has an R0 in the vicinity of 2.5 ( https://www.cdc.gov/coronavirus/2019-ncov/hcp/planning-scena... ). In the meantime, public health measures like masking and distancing will work against both viruses. If…
It's conspiracy theory by definition if it falls outside the official narrative. So even science can be a conspiracy theory. In fact, real science has a tendency to be viewed (by non-scientists, it should go without saying) as conspiracy theory insofar as it challenges the official narrative, and invokes complicated explanations, rather than a nice simple answer.
In this overall thread, the idea that the "disappearance" of flu is driven by political desire to label all respiratory illnesses as covid cases would be an example of a conspiracy theory.
Another commenter brings up the idea of 'viral interference.' This is not an example of a conspiracy theory, but I do not give the idea great credence on Occam's Razor grounds.