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In Legends Darth Plagueis was still alive around the time of TPM before Sidious killed him.

Has new canon given any answers about when his death occurred?

Not really.

Though Queen's Peril(which is set right before TPM) does heavily imply that Palpatine and Maul are the only two Sith who were around at the time. So I'd guess he killed Plagueis a good bit before that.