How are digital signatures secure?

Hey everybody, I’m currently trying to learn about digital signatures for my essay on how cryptocurrency transactions work but I’m lost. I understand what a digital signature is but I don’t understand how it’s secure. I mean this: Let’s say I want to send my document to my friend James. What videos have been saying is I run the message through a hashing algorithm. This produces a digest which I use twice once to encrypt using my private key forming the digital signature and another time encrypting it with his public key so only he can access it. I send them both off together. So ok. I get how he verifies it comes from me by comparing if the digests are the same, but doesn’t that risk how the information is safe , as if a miner wants to validate it comes from me he can use my digital signature to decrypt the message and then run it through the same hashing algorithm that Bitcoin uses and gets access? Essentially, are Bitcoin transactions confidential or not, as if they’re confidential wouldn’t using a digital signature if decrypted show you how much was transacted between two wallets?

submitted by /u/lilxskeet
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source https://www.reddit.com/r/btc/comments/qggeyf/how_are_digital_signatures_secure/