Flynn effect is measuring increases in education, thus people are better more familiar with the content on IQ tests before they actually do them, thus they do better, despite no genuine increases in general intelligence . James Flynn calls this event "scientific spectacles". Different subtests are more prone to these. For example some IQ subtests tests you can increase your performance by practicing them, or doing similar tasks that carry over. Meanwhile some are more immune to any performance increases. Any rises in IQ test performance, so the Flynn are only found in the more environmentally impressionable subtests called the Jensen effect (more precisely the Jensen effect just means More g loaded the task = More heritable the performance on the task)
When looking at performance on the more innate measures of intelligence (which includes per capita rate of major innovations per year), There is a clear decline in performance since the 1850's (called the Woodley effect). Furthermore less intelligent people have more children, and the gene frequencies of particular genes found in Higher IQ people have been decreasing per year indicating ,for genetic reasons, general intelligence should be going down. Simultaneously we have the increases in the environmentally impressionable components of IQ test to mask the genetic decline in intelligence (called the co-occurrence model)
I would provide sources but I couldn't be bothered. You can look up all the effects and model shit on google, you will find plenty of sources.
Also pic related is us by the end of the century, that or we're all dead.