I wonder if one mechanism is that the pandemic has affected everyone - some people worse than others of course, but we're all affected, there is this THING that we have in common with everyone else.
With the pandemic you can find someone else going through the same sort of thing, they will have empathy about their shared experience. For most people this level of isolation is temporary however, for the disabled this is their every day and they also on a day to day before the pandemic they didn't have this empathy from anyone, from their family nor their doctors. It is about the best it has ever been for the chronically ill, people for once have some empathy for what they are going through but I suspect it wont last.
I suspect pretty much every "mental health" issue will at some point finally be tracked to a physical condition, potentially something we could have been treating decades beforehand if they had bothered to look.
I don't know what underpins PTSD, I just know I wouldn't jump to any conclusion. I would want researchers to never stopping looking for answers until we genuinely understand what physically is going on in those individuals bodies. Talk therapy has too long been used to paper over that understanding and tried to tell people they are really just well if they thought differently and I am not convinced that Psychology should be funded as medicine given how it gets it wrong more than it gets it right and can't even get its diagnoses straight. Gulf war syndrome is a physical condition, it is basically PVCS/ME/Fybromylgia but for decades it was considered Psychological. I am constantly appalled by medicines practices.