Hi Tom,
I think the thing to focus on would be the LOW overall risk even with the Covid infection. Like Shin stated, a very low risk DOUBLED, is still a very LOW RISK.
The development of "schizo" isn't set at birth even with an increased risk. Again, as Shin discussed, there are lots of other infections in pregnancy that also discernibly increase risk. Covid may wind up being less significant than other background illnesses
that have been around for decades.
Plus, there isn't anything you can do proactively to prevent schizo. Their child will be perfectly normal in every way. Worrying about it and being hyper-vigilant is more likely to create the "stressful childhood" you want to avoid.
The "danger period" won't happen until they are in their 20's. There are so many other possible risks with higher likelihoods of occurrence.
Focusing on this one thing is like obsessing over one tree in the forest because your attention got focused on it and ignoring all the other much scarier trees that could fall on you.