(Using made up numbers here)

Lets say that infection #1 puts the risk of outcome A at 40%

Infection #2 puts the risk of outcome A at 60%

Infection #3 puts the risk of outcome A at 70%

Each infection increases the risk of outcome A, but it isn't an increasing rate.

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This would be very different from

Infection #1 having a risk of outcome A at 10%

Infection #2 having a risk of outcome A at 30%

Infection #3 having a risk of outcome A at 70%

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The first case that I described matches Figure 5: https://www.nature.com/articles/s41591-022-02051-3/figures/5

Note the difference in the rate of increase between the infections.

Yes, multiple infections increases the risk. However, each subsequent infection has a lower rate of increase of the chance.

Or, as a more dramatic example, suppose infection #1 gives a 50% of long Covid. Infection #2, in a patient without long Covid, gives a 1% risk of long Covid. Your cumulative risk of long Covid after 2 infections is 50.5%, which is greater than 50%.