Thanks for the response, Seeyan. That is an interesting point on philosophical nihilism's historical antipathy towards modernity, although I would argue the term has no cultural purchase today in this context outside of academic philosophical contexts.
As for logging off, I would agree that logging off in and of itself is little more than temporary cessation as you say. What matters is what one does upon logging off, but crucially, this step cannot be realized without disengaging from the internet's stupefying and simulated incentive structures first.
I also don't think the internet is the main driver of existential despair. That would be capitalism. However, more and more as the internet is sublimated further under capitalism, it serves to reinforce the atomizing and harmful pathological currents that underlies capitalism. In Gramscian terms, the internet exists as a part of the superstructure and mutually reinforces that of the economic base.
I would also push back on the sentiment that being online constitutes "the core of the 21st century lifestyle." This seems to naturalize conditions that are, to me, by no means natural or necessary to/for our species being.