I think it will boil down to people leaving the internet, caused primarily by platform decay. The regular person realizes they are wasting their time looking at ragebait, ads and propaganda. The algorithm will no longer be able stimulate the user in a way that keeps them hooked and genuinely engaged. The influencers will be the last ones to quit, as they will be getting "engagement" by bots while regular users - mostly viewers who don't post or comment much - keep steadily leaving, also taking their friends and family with them.
Edit: I will add a bit of hopefulness:
I do think social media advertising has a bit of a bubbly vibe to it, I think the effectiveness of social media advertising is highly exaggerated. I can see internet advertisements get scaled down in the future, thus keeping the mainstream internet going for a few more years longer than if they keep up the current levels.
I am also feeling hopeful that the internet has helped people find offline hobbies easier, so leaving the internet will be easier and less socially devastating. People are getting ready to go outside.
Final edit:
I don't think internet will ever fully, permanently end. It has connected so many people from across the world based on so many different interests. For example, internet based gaming (selling, sharing, developing and playing together) is such a big and popular hobby, that there is no way in hell it will go away ever. The mainstream internet (meta-platforms, reddit, youtube, etc) will probably loose majority of their human users in the future, but as a whole I don't think internet will ever loose 100% of its users.