Play chess. There are many free sites and apps. Start on low levels and when you're winning better than half the games, move up a level.

You will be amazed at the cognitive improvement from a handful of games a day. If you have the time, play a few games in a row until you get a mild headache. The headache if you get one is blood flowing to areas that haven't been used in a while, or at all.

Video games are high speed puzzles and very good for cognition, but chess has withstood the test of time and greatness. Play slightly better levels than you're at and you have to improve. Both your hardware and software will improve.

If you've been stuck in a rut, break out of it. No one can help you more than you can.

I use this, but have no preferences or affiliation. I'm making progress both in the game and in my life, which was petrifying before my eyes.

https://lichess.org/

Play chess. It's good for you and will help.