Some of my files have been encrypted by ransomware. I can find some backup of files (unfortunately not all of them). Can I find the password of the 7Z zipped+encrypted files if I also have some of the original files?
7z uses AES-256 with the CBC mode of operation for encryption. Since AES in CBC mode is resistant to known-plaintext attacks ( The CBC mode has greater security than KPA, it has Ind-CPA), having the original files will not assist you in cracking the key/password used for encryption.
mti2935 and Adam Katz point out that 7z used a broken IV generation mechanism up till 2019. While detrimental to secrecy of the encrypted data, as far as I can tell, it only leaks information about the plaintext. I'm not a cryptographer and can't state this authoritatively, but I don't think the weak IV enables attacks against AES that would allow recovery of the key/password faster than brute force. (Edit: Someone with sufficient cryptographic knowledge has commented, confirming that the attack on weak IVs is not a key finding attack.)