They explicitly call out the summer holidays effect above the first graph: "Generally, MAU fluctuates over the course of a year, dropping in the summer months and during holidays." So comparing the peak of Jan 2019 to the low of Jul 2021 isn't giving a good idea of the total loss.
Jan 28 2019: 253.9M
Jan 27 2020: 229.5M
Feb 01 2021: 219.7M
Jul 22 2019: 224.2M
Jul 20 2020: 214.1M
Jul 19 2021: 200.4M
Still, definitely not good; we've seen what happens when web developers believe only a single browser (engine) matters, and we _need_ an organization like Mozilla, which puts user interests above commercial interests, to have a seat at the table.