To do this, use the button on the top-right (the two overlapped squares) It was not very obvious to me, always assumed that it was for fullscreen or something, I had almost given up looking for it when I moused over it as a last ditch effort.
The most current BIMP will allow you to use gmic, make sure you install G'mic and then BIMP while GIMP 2.10 is not running, then start GIMP.
I am still in the dark about log output, haven't found that one yet. Thanks to SEO there is no more exact match text searches, so finding exact documents... a dying niche.
If you are new to G'mic, check out some of the neat plugins (dream smoothing is pretty cool, as is the line art and AI line art color fill)
If you have the desire to do so, I urge you to write more presets :) we can't get enough.
This is tested on Gimp 2.10 and Win 10.0.0.19044.2604 (x64) and (XLK)ubuntu 22.04
Use at own risk/discretion!