(I am unsure where to report a bug. There is a 'report a bug' menu option - when one is playing a game versus the computer - but that button does not work for me.)
So far as I can see, enabling 'allow takebacks' within the 'custom' play-vs-computer settings (and that is the only setting therein that I enabled) did not actually allow takebacks. For, subsequently I saw no facility to take a move back.
Firefox 121.0 x64
Windows 10 Pro - 22H2 (2009: 19045)
You just use the arrow keys to move back.

(I am unsure where to report a bug. There is a 'report a bug' menu option - when one is playing a game versus the computer - but that button does not work for me.)
So far as I can see, enabling 'allow takebacks' within the 'custom' play-vs-computer settings (and that is the only setting therein that I enabled) did not actually allow takebacks. For, subsequently I saw no facility to take a move back.
Firefox 121.0 x64
Windows 10 Pro - 22H2 (2009: 19045)