The computer is real fast right now and later, lots of passwords can be cracked by brute-forced or dictionary, and I also hear that cracking 7zip pakage with password protected is very impossible if your password is strong. So despite setting a strong password, I ask for a software which crypts my files safe from brute-forced.
You can’t protect an encrypted file from bruteforcing. That’s why you need a very long and complicated password. Also don’t use anything other than GPG for symmetric encryption - their implementation has been heavily studied.
There are so many algorthms, only symmetric encryption is best?
AES-256 is standard.
but many great softwares using AES-256, not only GPG, or not using symmetric encryption?
I think there’s some confusion. Symmetric encryption means you unlock it with a password. Algorithms like AES (but not limited to it) are used to implement symmetric encryption. AES-256 happens to be the best studied standard on Earth and so its recommended to use it.
OK, get it. I also read about Veracrypt, https://www.veracrypt.fr/en/Encryption%20Algorithms.html there is a key size list for algorithms, AES is one of the 256 bit, AES-Twofish-Serpent has 256; 256; 256, has more values than single AES, is AES-Twofish-Serpent more secure? Any other algorithms has the keysize/ Block Size more than 256 bits?
256 bits are more than enough if you read up on it to find why.
A cascade of ciphers is theoretically more secure but can be more prone to coding errors which can reduce security than using just AES.