It’s a common misperception that having multiple records of the same species, or even same individual organism, on different platforms causes problems for researchers. Researchers are basically not going to use these sorts of data to estimate abundance. At most, they might use the data to identify encounter rates - which species are recorded more often by people than others - but duplicate records are the least of their problems.
The bigger problems for researchers are inaccuracies and imprecision in recording location (e.g., if multiple people photograph the same organism but record it at different coordinates, which is common on both iNaturalist and eBird, for example); misidentifications, whether from computer vision or otherwise; taxonomic mismatches; lack of observer coverage in large areas; and other sources of error and bias. These can cause headaches when analysing citizen science data, but duplicated valid records of a species in a location are not a problem.