The immune system works best when there is a fever and if you suppress it you are just trading long term complications for short term relief. In the Covid-19 case it would IMO be much better to drink lots of fluids and just let the fever run its course.
I'm not a doctor so you shouldn't listen to me, listen to the awesome Dr Campbell instead, https://www.youtube.com/watch?v=gJqSdmNNwW4