A request to support a claim about the "long term" effects of a virus/disease discovered less than 2 years ago, in a rapidly changing environment, for which it seems pretty improbable for there to have already been robust, repeated, falsifiable studies done, is different.
I would also suggest that if you want "robust, repeated, falsifiable studies" for "effects of a virus/disease discovered less than 2 years ago" you have set your standard implausibly high. That's not how medicine progresses for urgent things, because it's fantastically negligent. Contrast the rapid global Covid response, which saved millions of lives, with the incredible foot-dragging surrounding AIDS in the 80s. If we had waited for perfect knowledge before taking action, hospitals would have been stacking bodies in the streets.
At this stage you get papers saying things like, "A quarter of children experienced persistent symptoms months after hospitalization with acute covid-19 infection, with almost one in ten experiencing multi-system involvement. [...] Our findings highlight the need for replication and further investigation [...]". [1]
[1] https://erj.ersjournals.com/content/early/2021/06/10/1399300...
Long COVID isn't well-defined in general; some large subset of it is psychosomatic. The main non-psychosomatic problem seems to be fallout from ARDS (Acute Respitory Distress Syndrome), which is directly related to severe bouts of COVID (and generally younger people have less severe COVID, with or without vaccines).
https://www.statnews.com/2021/03/22/we-need-to-start-thinkin...
Asking a source for an imprecise, sensational-sounding claim doesn't deserve this level of hostility.