Flu kills tens of thousands of people each year in the UK. Long term problems it can cause include inflammation of the heart (myocarditis), brain (encephalitis) or muscles (myositis, rhabdomyolysis) tissues, and multi-organ failure.
I know of people who have had ME-like symptoms for many years after a dose of the 'flu and I myself was unable to work for 3 months afterwards and fell into bed early for a good year, although I was young and fit.
Many years some hospitals are nearly swamped with flu patients, emergency status is declared. But for many people with a dose of flu will not even need to stay in bed.
There's a vaccine for flu, which is more effective against some variants than others. Flu mutates rapidly.
Whereas Covid ...?