The seasonal variation you see is to do with the plant uptake during the year, and the relative differences between northern and southern hemispheres of land and sea.
First, the significance of spring is related to the shift of terrestrial plants from barren winter branches to bountiful spring leaves. After the leaves on the trees drop in the fall, the leaf litter and other dead plant material break down throughout the winter thanks to the hard work of microbes. During this decomposition, microbes respire and produce CO2, contributing to atmospheric CO2 levels in the process. Thus over the course of the winter, there is a steady increase in CO2 in the atmosphere. In the spring, leaves return to the trees and photosynthesis increases dramatically, drawing down the CO2 in the atmosphere. This shift between the fall and winter months to the spring and summer results in the sawtooth pattern of the Keeling Curve measurement of atmospheric CO2 such that every year there is a decline in CO2 during months of terrestrial plant photosynthesis and an increase in CO2 in months without large amounts of photosynthesis and with significant decomposition.
May is the turning point between all the decomposition throughout the winter months and the burst of photosynthesis that occurs with the return of leaves to the trees in spring. CO2 measurements all over the globe reflect this pattern of peak CO2 concentration occurring each May, regardless of the level of that peak. Atmospheric CO2 has reached daily peaks of 400 parts per million for the first time this year as a result of the upward trend in CO2 overall, and the first monthly peak will likely occur in May.
While it is spring and summer in the Northern Hemisphere, it is fall and winter in the Southern Hemisphere, so why don’t these signals of photosynthesis and respiration cancel one another out? For one thing, the mixing between the hemispheres is too slow for there to be much interaction between their two cycles. It takes roughly a year for the air to mix between the Northern and Southern hemispheres. The mixing within each hemisphere, in contrast is only weeks to months. This is why a similar cycle is seen at all our Northern Hemisphere observing stations regardless of their latitude. There is a much larger amount of land in the Northern Hemisphere, particularly with huge forested areas in Siberia, while the Southern Hemisphere is dominated by ocean, but because of the slow mixing, even if there were as much land in the south, the Mauna Loa cycle wouldn’t look very different.
https://scripps.ucsd.edu/programs/keelingcurve/2013/06/04/why-does-atmospheric-co2-peak-in-may/That will continue as before; on top of that, we may make a decrease in the annual man-made input. That will take months before it's visible against the yearly cycle (and how much our emissions are down is yet to be seen; we're still heating homes, and some workplaces, and there's some travel going on; and air conditioning will still get turned on soon in some northern hemisphere locations).
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