If I have an issue with thousands of lines, i.e., and hit the edit button, and the option fit-textareas is enabled, the text box area is expanded and the save and cancel button are hard to reach.

What are you suggesting as the work around? Not applying the box on edit functionality? I personally use the keyboard shortcuts and never hit the buttons.
Maybe limit the maximum size?
Also, I kept trying to hit Esc key, but it did not work to cancel it, it just did nothing.
I feel the pain. Here are 2 solutions that don't involve setting a limit:
esc should press Cancel or blur the field, this is actually already a feature of RGH and it isn't working (at least in this case) https://github.com/sindresorhus/refined-github/blob/0b6c7330c21f8570519143ad3d0decc328d4db47/source/features/comment-fields-keyboard-shortcuts.tsx#L33-L45blur, which coupled with esc-to-blur could also fix it, but I think I want the field to _always_ fit the content.So I think if the esc-to-cancel feature if fixed (or extended to edited comments), then this would at least fix the specific use case.
I just disabled the setting and it seems more than enough because GitHub by itself, already auto expand the edit box size up to a page size and it seems more than enough.
I just do not understand why this problem happened rigth now. Did you add this fit-textareas setting recently? I looked over the changelog and could not find any mention of fit-textareas.
The changelog mentions it as “Comment boxes expand with their content and no longer show scroll bars”
Replaced with a more specific issue: #2413
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The changelog mentions it as “Comment boxes expand with their content and no longer show scroll bars”