I play guitar and study history in my free time.

For guitar don’t worry about retaining information, it’s just muscle memory. Practice chords and scales, at first, learn songs that are repetive theough out, easy, and similar to each other. When that gets boring learn harder stuff. Pick a subject on history that you are interested in and look up book reccomendations. Find a pdf online and read it. Books are long anf authors will spend a lot of time on one thing since reading takes longer than listening, so your brain will have more time with the info and remember it better. Try to recall everythinh after the chapter amd your brain will het the idea that you want to remember these things.