I’ve never seen a claim that Jenkins is compliant with WCAG 2.1, though there certainly have been many times when accessibility issues have been reported and resolved.
We’ve had at least two cases in the past where a company performed an accessibility assessment and submitted the accessibility assessment as a Jenkins issue that others could reference.
I encourage you to do the same. You can consider it a way for your company to support the Jenkins project and benefit other users. Pay someone to do the assessment so that you have the assessment. Then you can share that assessment with the community so that others benefit from it.
The March 2023 Jenkins UX SIG noted that there were efforts to achieve WCAG AA compliance, but I have not seen any report. I’m not aware of any other report or documentation focused on WCAG.