I believe there's a time limit on how long after an incident action might be taken. Proving any type of negligence is almost impossible.
Last year, I was on a ventilator with Covid. After a week, the hospital took me off it to see if I could breathe unaided - after a day, they decided to put me back on it. They needed to sedate me (put me into a medical coma again). They injected me with the wrong stuff- Adrenaline. It sent my BP to 350 top figure. The error was rectified shortly afterwards, then a day later it was found that I'd had a stroke (5 blood clots, actually). I was in hospital for a further 4 weeks.
This was all told to me over the 'phone, 2 months later, when I was at home. An investigation was made, and I received the written 5 page report. They said the stroke was caused by Covid - no other reason for my stroke, they said (non-smoker, no hypertension, etc). I contacted 3 "no win, no fee" places - none would take on the case, as they said the NHS had already concluded their investigation.
In my experience, it's virtually impossible to sue the NHS.