I found the man and he gave me 5 more addresses with PK like the one in the txt file, all around 0.5-1.1 btc on it.
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He is a bit dementia
I guess he didn't know he gave you a quarter million dollars?
cant remember how they make the bitcoins to money, but all happend on a pc with a Bitcoin Core software he had
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What i figure out with all the PK i saw is
53 Characters
hex format
no big I or big O letters
Crazy idea: get Bitcoin Core, or even an older version that was around when those keys were created, install it on an offline system, and try to somehow import these keys.