I don't know, when I read US PhD students posting in academic Twitter I'm under the impression that they have to pay huge tuition and go into debt, can barely subsist, are exploited for teaching and can't even do much research, and are often on the brink of depression.
I assumed reality would be somewhat less grim as my sample is probably biased towards the ones who complain, but maybe it's so biased that it doesn't even resemble reality at all.
There is professional school (med school, law school, business school) and there are PhD programs. The former do cost quite a bit in the US, but Ph.D programs in the US (at least in the sciences) don't cost anything if you get in and in fact pay you a salary (I have a doctorate in microbiology and that's how it was for me and everybody I know). That being said, this generosity has a dark side -- there are considerably more Ph.Ds produced than can have jobs in scientific research and that's because grad students are a source of cheap labor for professors.
I think it's true that many PhD students have less time for pursuing their own research interests than they would hope, it is very tied to your advisor's wishes. Brink of depression is probably not a huge exaggeration either, at least for a non-negligible subset.
Barely subsisting is definitely not true for a STEM PhD at a decent program though. You're getting paid way less than you could probably, but as long as you're willing to have a couple housemates (usually fellow students) and are not yet supporting anyone else it's a reasonably comfortable wage. Keep in mind that solid health insurance and student perks like university gym membership are also provided at 0 cost.
This might be controversial, but people who have excess expenses (for whatever reason) in their mid 20s probably shouldn't undertake a PhD in the first place. That's the only way a STEM researcher who didn't settle for a subpar school could possibly end up in additional debt as a PhD student IME.
Post doc wages, given the career stage and associated job culture/benefits, are notably shittier. Debt still feels like an exaggeration to me, but a 35 year old with a lot of training and unclear future career prospects should at least be able to support a middle class family lifestyle with their postdoc wages. A 25 year old that is working towards an actual degree and still benefiting from student status is such a different situation.
In hindsight, the maximally enjoyable thing might be to work for FIRE and then pseudo retire to being a PhD student. A PhD can be inherently valuable, the problem is just how tied it is to an insane career path.
Anyway, it's possible the posting students are humanities PhDs? At a good place they still don't pay tuition, but will often get basically 0 stipend. So they legit need loans for living expenses. Either that or Twitter amplifies complaints from schools that one really should not do a PhD at.
I assumed reality would be somewhat less grim as my sample is probably biased towards the ones who complain, but maybe it's so biased that it doesn't even resemble reality at all.