It has been a few years but before my father passed away I recall sitting at the computer with him and he was showing me a RMD he was making at Vanguard and I could have sworn that Vanguard has a recommended/suggested RMD he needed to make. That was August 2021.

While a brokerage may not know all of your assets, they would know your age and your $ amount in their brokerage and can easily calculate the amount you need to withdraw from them. Now if you have 4 IRAs and decide to do all of the RMDs from only 1 account, that would mess things up, assuming that is allowed.

I know for something like an inherited IRA Fidelity provides me a dollar amount I should withdraw. I do my own calculations as well.

Rich

P.S. I gave up on Vanguard many years ago and the hassles with inheriting my father's accounts just confirmed my decision. YMMV.