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> I needed to input my seed phrase
This is the biggest red flag of all red flags.
Think about it: why did you buy a Ledger Nano device in the first place? The only correct response to that question is „so that I don’t have to type my seed phrase into a computer“.
> I have been so cautious
Agree to disagree on this one. You committed the most obvious and glaring error of all time: you typed your seed phrase into a computer.
If the question is: „what is the most wreckless and obviously-not-cautious thing you could possibly do?“, the answer is to type your seed phrase into a computer.