There are some strange aspects of this particular tweet that surprise me from a nurse, but some of what it said is certainly true.
Friends of mine who are medics and can be trusted have been saying similar, and reporting seeing many young and fit people incredibly sick. There is a massive issue with people who are not really recovering even though they have not died. You might remember the doctor who treated Boris Johnson said covid could well be this generation's polio in terms of long term effects. I have also heard first hand from doctors working in ICU that the clotting is like nothing they have ever seen in decades of working as medics.
We also don't know the long term effects after mild illness. I hope there will not be any but some worrying suggestions have been made by relevant specialists.
It is also true that many have entirely misunderstood what is meant by 'mild case'. Someone who had pneumonia and is still struggling months later, but was not hospitalised, would be classed as mild.
Normally I would not like to say any of the above to someone who has health anxiety, but since this is a public forum I don't want to lie. Keep in mind though that there are definitely many cases, maybe more than we even suspect, where people experience no symptoms or symptoms we would genuinely call very mild. Also that there are many other things we risk all the time that could damage or kill us, but we are used to that risk and don't dwell on it. So you don't necessarily need Covid cases to be at zero before you can feel comfortable to resume more normal activities. The cases the tweet mentions are at the severe end of the spectrum and you'd be very unlucky to end up in that position.
I don't know if I have had COVID, but I did lose my sense of smell completely for several weeks and had very minimal other symptoms. If it was covid, then there may be long term effects I don't yet know about, but it was incredibly mild at the time. I am over 40, overweight and quite unfit with an underlying condition. Depressing description of self there but not untrue sadly.