Darrin, that's easy to explain.
The atmospheric CO2 level is determined by the combination of all the fluxes of CO2, into and out of the atmosphere. Mankind's net fluxes are currently adding about 5 ppmv CO2 per year, to the atmosphere. Nature's net fluxes are currently removing about 2½ ppmv CO2 per year. The difference is the rate at which the amount of CO2 in the atmosphere is rising: about +2½ ppmv per year.
However, normal, transient fluctuations in natural CO2 fluxes cause large year-to-year variations in the rate of atmospheric CO2 concentration increase. Those fluctuations are considerably larger than the change expected due to the Covid-19 recession.
Consider the measurement record for the last decade, from annually averaged CO2 levels measured at Mauna Loa:
In 2010 CO2 level was 389.90 ppmv, an increase of 2.47 ppmv over the previous year.
In 2011 CO2 level was 391.65 ppmv, an increase of 1.75 ppmv over the previous year.
In 2012 CO2 level was 393.85 ppmv, an increase of 2.20 ppmv over the previous year.
In 2013 CO2 level was 396.52 ppmv, an increase of 2.67 ppmv over the previous year.
In 2014 CO2 level was 398.65 ppmv, an increase of 2.13 ppmv over the previous year.
In 2015 CO2 level was 400.83 ppmv, an increase of 2.18 ppmv over the previous year.
In 2016 CO2 level was 404.24 ppmv, an increase of 3.41 ppmv over the previous year.
In 2017 CO2 level was 406.55 ppmv, an increase of 2.31 ppmv over the previous year.
In 2018 CO2 level was 408.52 ppmv, an increase of 1.97 ppmv over the previous year.
In 2019 CO2 level was 411.44 ppmv, an increase of 2.92 ppmv over the previous year.
The average annual increase over that ten year period was 2.401 ppmv. But it varied from as little as +1.75 ppmv to as much as +3.41 ppmv.
Mankind added about 5 ppmv CO2 to the atmosphere last year. The Covid-19 slowdown might reduce CO2 emissions by 5 to 10% this year. Even a 10% reduction would make a difference of only about 0.5 ppmv in atmospheric CO2 concentration. That would be very hard to notice compared to the larger normal fluctuations.
A related question is the cause of the ongoing atmospheric CO2 level increase. Some people think it is from ocean outgassing. They're wrong. You can read about their mistake here:
The oceans are not warming enough to have much effect. We know from ice core data that the decline in temperature from MWP peak to the bottom of the LIA reduced atmospheric CO2 level in Antarctic ice cores by only about 9 ppmv, in 450 years, which is a rate of change averaging only about 2 ppmv per century. Likewise, the difference between interglacial peak CO2 levels and glacial maxima CO2 levels is only about 90 ppmv, from the combined result of ocean temperature changes, ice sheet burial and probably other mechanisms. Here's a paper:
Here are Law Dome (Antarctic) ice core data, back to year 1010. Scroll down to "CO2, 75 Year Smoothed", then keep scrolling. Watch CO2 levels climb to their peak of 284.1 ppmv circa 1170 (MWP), and fall to their lowest level of 275.3 ppmv circa 1615 (LIA):
The temperature decrease from the MWP peak to the bottom of the LIA caused a CO2 level change of only about 8.8 ppmv.
Since then CO2 levels have increased by about 138 ppmv.
Unless someone thinks that the current climate optimum (warm period) is (138/8.8)= 15 times warmer, compared to the worst of the LIA, than the warmth of the MWP, it should be obvious that the recent warming cannot have caused the CO2 level increase.
The reason the amount of CO2 in the atmosphere is rising is simply that we're adding CO2 to the atmosphere faster than nature is removing it. However, the rate at which nature removes it accelerates as the level rising, so dramatically that we can calculate that the atmospheric CO2 level would plateau at only about 500 ppmv if CO2 emissions continued at the current rate. That's called "negative feedback."
Physicist Clive Best explained it like this:
“It is like pumping air into a tyre with a puncture: the harder you pump the faster the air escapes.”
You can read more about it here:
CO2 since 1800SEALEVEL.INFOCO2 since 1800