How do I know the main idea/summary of informative non-fiction books without plots? I have too many books and I'm trying to declutter.?

Hello everyone, so I've decided to Kon-Marie my bookshelves and boxes of books in my closet, because: 1 they are taking too much room 2 I've bought many at discount prices, but I'm too busy to read them I'm not in a hurry to declutter my room, but decluttering them would bring more positive vibes... show more Hello everyone, so I've decided to Kon-Marie my bookshelves and boxes of books in my closet, because:
1 they are taking too much room
2 I've bought many at discount prices, but I'm too busy to read them

I'm not in a hurry to declutter my room, but decluttering them would bring more positive vibes into my room.

I am planning to take notes of the main ideas of these books and sell/donate them, because I've invested money into them in hopes to read/understand them.

Any tips on how to skim through the books for the main points/summary to take notes? The type of books I have are popular non-fiction titles such as:
"Thinking Fast and Slow" by Kahneman
"Think and Grow Rich" by Hill
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