Are the files encrypted with the 7ZIP password cracker vulnerable?

7zip password cracker is secure since it uses AES-256 in CBC mode that can provide CPA security and there is no problem there. Keep in mind that CBC has no integrity and authentication. The real problem comes from the human side; the password!  7zip uses 219-times iterated SHA256 to derive the AES-256 key from passwords. SHA256 is not a memory-hard function and therefore this is not safe from massive parallelization. The collaborative power of Bitcoin miners can reach around 292 double SHA256 in a year. A single Nvidia RTX 390 can calculate 9502.7 MH/s... Therefore one needs a really good password mechanism to be secure from the password list/guess/search attacks.

A password with high entropy generated from diceware is recommended XKCD. Use a password manager like keepass that handles this for you.  Additionally; You need to transfer the password to the other party this means that you need a secure channel to do this. A signal program is a good candidate, or you can go for Diffie-Hellman Key Exchange (DHKE), better its Elliptic curve version (ECDH) to establish a key, and then use a key derivation function to derive a long password.