Physically - Watch my one year old grandson 3 days a week, 9 hours per day. Lots of lifting, carrying, walking, pushing a stroller and other physical exertion. On off days, I try to get a good walk in when the weather is cooperative.
Mentally - I still work part time from home and my work requires simultaneous intense concentration and multi-tasking. Seems contradictory but is nevertheless true. In addition to online articles and the news, I read at least an hour a day. Also do quordle, octordle and crosswordle puzzles before bed at night because word puzzles relax me.
Numerous articles about preventing Alzheimer's and other mental deterioration suggest "exercising one's brain" via puzzles, etc., are of little value outside of the enjoyment of the activity itself. What we mostly accomplish is improved ability to do that particular activity. So daily crossword puzzles makes us better at crossword puzzles, but don't do a thing for skills at, for instance, sudoku.
The best way to preserve cognitive abilities appears to be with good overall health including low BP and cholesterol numbers, minimizing sitting for long stretches, sufficient sleep, and physical rather than mental exertion. Working or exercising until slightly breathless is often cited.