Documents for an upcoming meeting of the Los Angeles Convention and Tourism Development Board (found by a poster on the Resetera forum) list E3 as a "Cancelled live event in 2021".
E3 2020 was cancelled due to the Covid-19 pandemic, and while the ESA looked for ways to replace it with an "online experience", in the end nothing came of it. Earlier this year the ESA suggested said that, "we are transforming the E3 experience for 2021 and will soon share exact details on how we're bringing the global video game community together" and the above document contains the note, "Working with production team on broadcast options at LA Live/LACC". While it's certainly possible an online version of E3 might come together, even before the pandemic Sony had left E3 to host its own event, and thanks to 2020 the likes of Ubisoft and Bethesda now have experience holding showcase events independently.
The Convention and Tourism Development Board document notes that they are, "Working on 2022 and 2023 license", but there's a chance that if things don't come together this year we simply won't see E3 return.
Last year we held our regular PC Gaming Show as an online event with more than 50 games on show.