But in electrum there are 2048 words that are public so we can consider that each word is 1 alphabet letter so brute forcing a 12 character password from 2048 pool doesn't seem that hard to do?
And after the seed is used is it possible to force it to use user generated password for make any transaction or after someone gets seed they have full access
You didn't read the post, did you? The search space is massive, in fact much more so than a 12 character password. Read the post and look at the math.
Electrum's mnemonic is similar to BIP39 but not the same. AFAIK, Electrum actually uses 13 words. That means that there are 11,150,372,599,265,311,570,767,859,136,324,180,752,990,208 possible combinations. Furthermore, there are 5 languages, so if you don't know the language, there are 55,751,862,996,326,557,853,839,295,681,620,903,764,951,040 possible combinations. Because the seed is random, there is no pattern, so the only way to get the seed is through brute force. Even if you were able to guess 50 Million seeds per second, it would still take 1.3274253094363466155676022781338310420226438095238095... × 10^31 years to go through the search space.
