It makes a lot of people dumber -- they doom scroll, gossip, play childrens games, and on the high end post cat memes.
But it's a tool like any other and the results depend on the user.
For those with eyes to see and ears to hear it is (was) the Library of Alexandria. The knowledge of the world unfiltered without gate keeper trolls deciding what you can see and learn.
Getting on the internet in 1993 completely changed my life. Linux changed my life and without the internet there is no Linux. Before Linux you could not get a UNIX distro for less than $1000 USD which was a lot of money for me back then.
Before Linux and Internet all that was available to consumers outside of big institutions was Windoze and Apple was already on life support. The internet and Linux opened an entire world to me and I never looked back. Everyone at the time said I was wasting my time and should be doing an MCSE LOL but those are people in the 90%... they will NEVER get it.
Fast forward 4 years later I'm working in startups and leading dev teams and that was almost 30 years ago.
I can imagine what my life would have been without the internet and I prefer how things worked out.
So it did not make me dumber... but the filtered nannied corporate approved internet of 2026 -- that probably just makes anyone dumber.
The Internet doesn't make people dumber any more than video games, rock music, picaresque novels, the printing press, or writing did. These kinds of arguments come around with every new technology and have always been fatuous.
The peak of human civilization, for me, was downloading Shrike and actually having it work "out of the box". If an absolute moron like me could get that to boot up with next to no involvement or fudging through the user manual, I knew then that the tide had turned.