I think the .log file is updated only after a successful login.
If you want to do manual brute-force guesses, go to Bitwarden’s interactive cryptography tool.
If your keyHash value is from later than June 9, 2021, you will need to save a copy of the HTML code of this webpage. Then edit Line 481 of the HTML file — change the third argument of the pbkdf2 function from 1 to 2, so that it looks like this:
self.masterKeyHash = await pbkdf2(newValue.arr.buffer, self.masterPasswordBuffer, 2, 256)
Now open the HTML file in any browser.
If your keyHash value is older than June 9, 2021, then you do not need to download and edit the HTML, just use it directly on the webpage.
On the form, enter your email, the kdfIterations value from the .log file, and your best guess at the Master Password. Compare the Master Password Hash that was calculated on the webpage to the value of keyHash. If they match, you guessed correctly.
Of course, it would be much more efficient to automate all of the above, which you can do using a tool like Hashcat.