I think barring especially extreme cases this is just the "television is ruining the world" of our generation. I'd describe myself as terminally online as I spend most of my time using the internet in some form.
Regarding use of internet slang, there's the fact that the Covid lockdowns helped accelerate a pretty massive shift in how we interact even with people we can meet in-person. Unless you're living with someone, the bulk of interactions with them are probably going to be online. Then, since you're online you end up using internet slang, which gradually bleeds into regular speech. There is nothing wrong with this.
There's also the issue that you're going to want to share your hobbies with people, which is hard without the internet if your hobby is kind of niche. Most of my hobbies are very niche, I have only ever known 1 person irl and 3 people online who had a similar enough set of hobbies. Even programming and working with electronics, which started as a hobby for me when I was 13-14, only developed because of the ability to find like-minded people online, away from my irl 'friend' group who only saw it as something to make fun of me for and parents who didn't believe in anything but schoolwork and perfect grades.
Overall, this post seems to be based on the assumption that people who are terminally online haven't put thought into their lives or that it's wrong to be okay with it. I can still unplug when having an interaction irl which I think is sufficiently important like with family (although somewhat ironically, the only way for me to interact with my family over the past 2 years was over the internet), but simultaneously, most of the people I enjoy talking to and can deeply relate to are only accessible online.
I get the impression that to the author, "terminally online" is equivalent to being someone who spends all their time getting into heated political arguments on Reddit and Twitter. While I did go through that phase too, I realized how unhappy it was making me and the solution wasn't disconnecting but rather identifying sources of bad content and disengaging. I got rid of all the default subs on Reddit, sticking only to ones related to my hobbies and being very selective about following more subs, same with Twitter. I also got much more selective about replying to things (eg I'll usually just ignore replies to my posts which I feel might devolve into an argument). The result was that the content that made me "ragescroll" went away and I got happier.