Before Google, search engines were basically just doing keyword matching and so you'd have the issue that every search for a programming topic landed you on expertsexchange. Google was the first to start leveraging click-away signal, and they were able to successfully down-sample keyword-farmers like that one and their ilk.
It was the worst. Crawling a ring all day to find useful content was incredibly inconvenient.
Independent of the elections I think social media websites had by this time “perfected” engagement-driven algorithmic feeds and online news had started getting good at optimizing their content for those purposes. And around this time, anecdotally, is when I think a lot of older people started taking the internet more seriously, as real-world services like Airbnb/Uber/Amazon prime (to be fair, started earlier) became popular and middle aged people started using social media more. This, in combination with the polarizing content of the elections, made the internet into the hostile and echo-chambery place it is today. And it also attracted a lot more Government attention leading to things like GDPR (good in theory, bad inasmuch as it led to the current cookie banner bullshit) and link taxes.
And with the beginning of the Ukrainian conflict.
But a lot of people will debate the actual overall influence of that vs it being a scapegoat used to delegitimize the right wing surge at the time; undeniably even if the right wing surge/political divisiveness trend was aided by Russian activity, it was still real people who engaged with it online and voted for the right wing causes.
The shift away from desktop and laptops to cell phones is a major factor as well.
To me 2016 was just a continuation of what started before, there was no inflection then.
The 2000's are when things started to change, not 2016. And Obama's first election was when the internet started to be taken seriously by politicians (2008). It's basically what gave him the win.