You ask whether estrogen that is “sent through your body” (systemic) causes increased risk of cancer and heart disease, and also whether topical application (localized) estrogen helps with brain fog.
This is an important topic, and complex, as well. There is a newly published book, Estrogen Matters, Why Taking Hormones in Menopause Can Improve Women’s Well-Being and Lengthen Their Lives—Without Raising the Risk of Breast Cancer, by Avrum Bluming MD and Carol Tavris PhD, that I think you should read. The synopsis is does neither: It doesn’t increase the risk of cardiovascular disease—in fact, it likely protects—, and it doesn’t increase the risk of breast cancer.
Localized/vaginal estrogen doesn’t provide any cognitive benefit (or bone or heart benefits, either); it is providing benefits to the vagina only. The products available for localized estrogen are all very similar in their risks (nearly none) and benefits (they all work very well), so I think the best option for each woman is dependent on cost, convenience, and consistent use. Select based on what you think is best for you.
And really, I do encourage you to read the book! It may give you additional factors to consider when evaluating systemic hormone therapy.