We tried both Windows Desktop Editor OnlyOffice (community version 9.1.0.167 x64exe) and Mac OS Desktop Editor OnlyOffice (community version 9.1).
While the Windows version can connect to our self-hosted OnlyOffice via Single-Sign-On, the Mac version got issue. The OnlyOffice server login page can be successfully reached in Mac version but upon clicking Single-Sign-On button, it gives a blank page as attached.
Our Single-Sign-On is provided by Keycloak which would forward the authentication to AD Federation Service, and a pop-up windows for user to login is expected. We suspect the Mac Editor blocked the pop-up windows, resulting in showing nothing.