Scripture is primarily about Spiritual matters. The day they became knowledgeable of good and evil and chose to do evil (by disobeying God) they cut off their special relationship with Him. Those who can only think literal and physical will tell you it is about dying physically.
Adam did IN FACT die """in the day""" he ate the friut
Genesis 2:
16 And the LORD God commanded the man, saying, Of every tree of the garden thou mayest freely eat:
17 But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
(NOTE: """IN THE DAY""" you eat from the tree of knowledge of good & evil, you will die)
Scripture teaches:
Psalm 90:4 For a thousand years in thy sight are but as yesterday when it is past, and as a watch in the night.
(NOTE: In Gods sight a day 1000 years is like yesterday = 1 day)
2 Peter 3:8 But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day.
(NOTE: With the Lord, 1 day is like 1000 years)
Genesis 5:5 And all the days that Adam lived were nine hundred and thirty years: and he died. (Adam died 930 yrs old)
According to scripture: Even though Adam lived to be 930 years old. He did in fact, die """IN THE DAY""" he ate the fruit.
Methuselah, the oldest recorded human lived to be 969.
Genesis 5:27 And all the days of Methuselah were nine hundred sixty and nine years: and he died.
Final thought:
The Day of the Lord in Joel 2:31 & Acts 2:20 isn't 24 hrs. It will cover 1000 years.