As an elite competitive triathlete, César Villalba, 34, of Los Angeles knows his body. So, though he can perform “acceptably” on a pulmonary test months after his initial bout with COVID-19, that’s anything but “acceptable” for the professional designer who is used to racing around the world. “I can do that with 60 percent of my lung capacity,” Villalba says with the heavy sigh of a man who would really just like to be better. Villalba was never officially diagnosed with COVID-19, because he got sick before the pandemic hit full steam. “I had pneumonia, sore throat, fever for a...