All the London railway stations :
Underground lines : Circle, District
I visited Mansion House station on the 4th May 2023. It is clearly not accessible due to lots and lots of steps. At least 47 steps, or 67 if travelling eastbound.
AccessAble Access Guide :
Accessibility friendly : Mansion House is not accessible to wheelchair users due to stairs between the platform and street level.
To access the booking hall is 24 steps.
In addition there are another 23 steps to the westbound platform, or 43 steps to the eastbound platform.