I've given this some thought. It really depends on what you mean by 'disappearing.' Living a whole new life in a different town/country I think is near impossible now unless maybe you're stupid rich. There was just that story about Ryan Borgwardt who tried to fake his death in a lake and fly to Georgia(European country). They were able to figure out what he did pretty quickly and now he's back in the US with legal trouble.
Disappearing domestically and living off the grid in the US seems a bit easier, but still tough honestly. You need your ID for so much -- hotel rooms, renting cars, anything. Plus there are license plate readers all over the fucking place now so disappearing in your own car isn't really feasible if you're using major us highways. So honestly it would just entail homelessness / camping really.
The most realistic kind of disappearing I think is just killing yourself in such a way that your body isn't found. Maybe taking a kayak to sea and dying by firearm a bit off the coast. Or hiking significantly off trail and maybe digging a little grave. You would still have to account for a lot like leaving your phone behind to avoid cell tower pings and your car and stuff, but I think this is reasonably possible.
For me the main desire to disappear like that is because I wouldn't want to burden my family with seeing and burying my corpse. Maybe that's a selfish desire though -- I feel like I often hear people talk about finding some comfort in laying their loved ones to rest. On the alternative you have people saying things like "oh consider all the first responders who will be traumatized by your corpse!" Ugh idk. This has turned into a bit of a rant but I do think about this topic pretty frequently.
Tldr: disappearing can mean lots of things, all of them require careful planning
