Interesting. The excess deaths from graph looks to be ~500,000 to 600,000, not the 1,000,000 that is claimed.
But you are correct, it's cumulative, so without Covid you'd expect max ~100,000 more deaths per year (aging population), so the baseline would be
2019 - 2.8M (+0 excess deaths)
2020 - 2.9M (+500k excess deaths)
2021 - 3.0M (+400k excess deaths)
So 900k.