Pleural effusions are rare in Covid. Covid can definitely trigger new breathing issues due to involvement of the lungs wherein there is progressing severe inflammation in the lungs, but unrelated to the pleura and the previous pleural effusion.
Next Steps
Seek immediate medical attention the moment you feel any kind of symptoms prominently fever sore throat bodyache diarrhoea loss of smell & taste and ofcourse breathlessness on exertion.
Health Tips
Try sleeping flat on stomach ie prone so that by gravity lungs fall forward and help maintain oxygen.
Also try a simple test. Walk for 6 minutes and observe if there is breathlessness. Can do this daily.