I couldn't find anything for this season, but the New Orleans Pelicans have the lowest three-point percentage by a team in a game with 20+ three-point attempts in 2019-20, at 9.4 percent against the Mavericks on December 7, 2019.

which team has the worst 3p% in a game with 20+ 3pa this season
Interpreted as:
Which team has the worst 3p% in a regular-season game with 20+ 3pa this season?

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