Software is in nuclear plants, cars, oil platforms, pacemakers, everywhere. If one is writing more ‘disposable’ stuff like flashlight apps for smartphones, then sure, as you say. Others are writing serious stuff, and design docs are invaluable.
For starters you're going to have traceability requirements that can only be satisfied if you have a product requirements document and then often a software design document. Now you might well choose to manage all of that in JIRA and Confluence (or whatever) rather than sitting down and writing an actual document intended to be laid out and printed on paper but the fact remains the documentation exists and, indeed, is a must to satisfy compliance and regulatory frameworks.
As always, the domain you're working in and the organisation you're working for make a huge difference but, as much as there are plenty of places where none of this stuff matters at all, there are also plenty of places where it's incredibly important and that isn't going to change anytime soon.
i can think of... zero times where a business-coded person even a technical PM (which is a role i do appreciate btw) has ever come up with an official design doc or specification that didnt suck. creating a good design doc is either going to require an architect/staff or senior engineer to sit down and just do it. the overworked architect or staff engineer inevitably gets dragged in if the developers hands are full, or they just beat the shit out of the developer and fill their calendar up with meetings and make them do it... then they beat the shit out of them again and make them build it.. then they beat the shit out of them repeatedly doing fast follows for months and say "no not like that"
i think everyone wants to take some pride in the org they work at and maybe they feel like they've got the formula for sucess, but i personally haven't seen it. there's always going to be an additional translation tax required of the developer(s) who is/are also building the damn thing at the end of it. cover it in poorly run agile/jira shenanigans and this just slows down the possibility of getting to a super stable state back soooo far.
i actually agree with the guy a couple posts up: do some loose design work, friggen dropkick/prototype and see where it lands and go from there. i like facepalm when i hear that our project guys were planning a project for a year and when it was finally time to move on it every specification they planned out missed all the details. this is totally so much worse now with AI writing everything everyone is putting together.
Documentation is important for platform, and probably nothing else.
I mean... when i was golfing, the cart had a gps enabled, cloud connected display that showed the golfers positions in front of us. I had a smart phone and a smartwatch with meter-accurate positioning to take a shot.
Software is beyond everywhere at this point.