There is some evidence that covid infection might be a trigger for dementia, especially in older adults. Studies have found that people who had COVID-19 who are over 65 have an increased risk of developing new memory problems or dementia afterwards.
It's thought that the virus causes inflammation in the brain or somehow damages the central nervous system, which can speed up the process of cognitive decline, as is seen in Alzheimer's.
It could be a coincidence, but I think it is more probable that it is connected.