This YouTube video from @LongCovidSOS (Twitter account created July 2020) is date-stamped 8th July 2020. You can't fake a YouTube date stamp.
International long Covid patient groups appeared in mid-2020.
The @long_covid Support Group created on Facebook on 2nd May 2020, Twitter in July 2020.
French LC group @apresj20 created a Twitter account in July 2020. USA group @Covid19Long Haulers did too.
The #longCovid hashtag was first used on Twitter on 20th May 2020:
UK Government NHS "Long Covid Recovery" video on YouTube date-stamped October 2020:
UK Government NICE: "COVID-19 rapid guideline: managing the long-term effects of COVID-19" (Long Covid), published in December 2020 following months of research. nice.org.uk/guidance/NG188
BMJ July 2020: Covid-19: What do we know about “long covid”?