You don't need to add fitness every single day.
You just need more days, weeks, months of fitness gain than fitness loss over the long term.
Take recovery when you need it.
Play the long game.
There are 4 key workouts that ALL humans should do regularly, regardless of sport or ability level:
Long - challenge the metabolism
Strong - challenge the muscles
Fast - challenge the nervous system
Recovery - challenge the ego.
@scullion262 saw your 2.09 marathon result and started digging through your training on Strava. Do you post all your runs? Impressive result off of lower, yet very quality, mileage