Check out https://www.kiplinger.com/article/retirement/T054-C000-S004-ira-qcd-rules-qualified-charitable-distr...
Bottom line for you: "Although Vanguard offers check writing, the firm requests that you either fill out a form or call to make the transfer for the donation to count as a QCD, says spokesperson Emily Farrell. Vanguard makes the check out to the charity and sends it to you to forward." According to the article, however, Fidelity will allow you to write checks with just a couple of caveats which are easily complied with.
