Jira doesn't have dark mode in 2022.
Very simple Chrome extension that applies 10 lines of css to Jira resulting in a very hacky dark mode.
Download the code or clone the repo, activate developer mode in chrome://extensions,
and load the extension using Load unpacked extension.
Will never be published to Chrome store.
This looks somewhat accessible to me but I am not a designer. Please feel free to improve and contribute in any way you know how.