This meme/copypasta originated on the 26th of January 2021, when Twitter user @plexie9 tweeted the following satirical tweet as a reply to a tweet from the president regarding a meeting between him and Angela Merkel, the German chancellor, about the COVID-19 pandemic:
"Dear Biden:
You are not my president.
You are not anyones president.
Donald Trump won the election and I think we both know that."
This got her a lot of replies, likes and retweets. Most of the attention was drawn from the left leaning side of Twitter, and there was little positive response from Trump-supporters or people who were anti-biden. This lead to the copypasta being used towards the presidents tweets in the following days, mostly done by Norwegian twitter accounts.
These are all the tweets with that exact same phrasing

Although there are probably some that have changed the wording just enough for it to not be in this search^

The most successful/annoying person who has used this copypasta is twitter-user @widxz with his total amount of replies being around 877. His most successful attempt so far