How the prediction was framed
Chamath’s claim was conditional: if there was a strong, coordinated effort to prevent voter suppression and mobilize young voters and people of color (e.g., efforts like LeBron James’s), then Joe Biden would win in a landslide.

1. Was there a “concerted effort” to prevent suppression and mobilize young/POC voters?

Evidence strongly indicates yes:

• LeBron James’s “More Than a Vote” was launched in June 2020 specifically to fight Black voter suppression and encourage registration and turnout, going beyond traditional celebrity GOTV efforts and using arenas as polling places and recruiting poll workers. (sportsbusinessjournal.com)
• Major civil‑rights and voting‑rights groups (e.g., the ACLU) mounted multi‑state litigation and advocacy campaigns in 2020 to relax or block rules that would disproportionately burden voters (witness/notary requirements for mail ballots, ID barriers, restrictions affecting Native Americans, etc.), explicitly framed as efforts to protect the right to vote during the pandemic. (aclu.org)
• Youth turnout surged: research from CIRCLE estimates that about 50% of 18–29‑year‑olds voted in 2020, an 11‑point jump from 2016 (39%), one of the highest youth participation rates since the voting age was lowered to 18. (circle.tufts.edu)
• Voters of color also turned out in record numbers: analyses show turnout among Latino voters up 31%, Asian turnout up 39%, and Black turnout up 14% relative to 2016, with Latinos and Asian Americans increasing their share of the electorate and total votes cast by voters of color hitting record levels. (catalist.us)

These data and documented campaigns match Chamath’s antecedent: there was a strong, organized push to combat suppression and mobilize young and nonwhite voters.

2. Was Biden’s victory a “landslide”?

The actual 2020 outcome:

• Biden won 306 Electoral College votes to Trump’s 232. (pewresearch.org)
• In the national popular vote, Biden won about 81.3 million votes (51.3%) to Trump’s 74.2 million (46.8%), a margin of roughly 4.5 percentage points and about 7 million votes. (pewresearch.org)
• However, his Electoral College edge depended on razor‑thin margins in three key states—Arizona, Georgia, and Wisconsin—where his combined margin was under 45,000 votes; flipping them would have produced a 269–269 tie. (pollbludger.net)

Mainstream electoral analysts do not characterize this as a landslide:

• PolitiFact, examining the same 306‑vote tally Trump once called a “massive landslide,” noted that 306 electoral votes rank in the bottom quarter of Electoral College showings historically and concluded: “It wasn’t a landslide, but it was decisive.” (politifact.com)

So Biden’s win was clear and decisive, but it does not meet the usual standard of a landslide, especially given how narrow the tipping‑point states were.

3. Evaluating the conditional prediction

• The condition (“concerted effort to prevent suppression and mobilize young/POC voters”) was substantially met: there were extensive national campaigns and litigation efforts, youth turnout jumped dramatically, and turnout among voters of color reached record or near‑record levels. (sportsbusinessjournal.com)
• The promised outcome (“Biden landslide”) did not occur by standard analytical usage; the victory is widely described as decisive but not a landslide, with historically modest Electoral College margins and very close pivotal states. (politifact.com)

Because the antecedent was effectively satisfied but the predicted magnitude of the outcome (“landslide”) did not materialize, the prediction, taken at face value, is incorrect.