> The final study population comprised 341 participants (90.6% females) who completed blood sampling and answered the questionnaire. A total of 232 (68%) were seropositive

How does this compare to the base rate in a similar population? Two thirds sounds like a reasonable estimate for "ever had COVID" in Denmark in 2022, though maybe a smaller percentage would in fact be seropositive. It would be interesting if self-reported long COVID had little or no correlation with having had COVID at all.

note that this is 'self reported long covid'. For a proper study you'd need an objective measure otherwise it can't be determined what might be long covid vs. fatigue from working late hours at work, changes in mood due to season, changes due to age etc.