So, one year later and the choline supplement has improved my cognitive function. I noticed it after a couple of months of the supplement. I kept taking it and have improved even more.
I took several bottles of Seeking Health Optimal PC.
Then I switched to Jarrow Neuro Optimizer, several bottles which I am finishing up now.
I am now switching to MicroIngredients Organic Sunflower Lecithin powder and will take 4 Tbsp. per day. If this doesn’t work for me I will go either back to Optimal PC or to alphaGPC.*
The Jarrow is cheaper than the Optimal PC. In the future I will look at the pricing on the Lecithin.
Or, egg yolks and liver. (Liver also supplies folate in force. Yolks also supply Betaine–and folate if the chickens eat grass and weeds i.e. "pastured" free roaming chickens. "Cage free" is a hollow term. Buy the best eggs you can; the yolks should be a dark, golden yellow.)
* https://chrismasterjohnphd.com/2017/08/12/living-with-mthfr/#dietary – more about the choline on this page on Dietary 4).