...
ADFS fully supports both IdP- and SP-initiated logout.
See: SLO: AD FS.
Azure AD
Azure AD has limited support for SLO.
While both SP- and IdP-initiated logout are reportedly supported, neither actually works. The result is that only basic SP-initiated logout is supported, which allows logout from AAD and the initiating SP.
See: SLO: Azure AD.
GSuite
GSuite does not support SAML Single logout as an IdP.
...
Keycloak fully supports SP-initiated Single logout, but to our knowledge does not support IdP-initiated logout.
See: SLO: Keycloak.
Okta
SP initiated logout is partially supported: The IdP and initiating SP's sessions are terminated, but other session participants are never notified.
...
The user is again redirected to Okta because Confluence has to initiate single logout (there's no way to know logout has already happened).
Okta now presents the user with a login form because the user already terminated the old Okta session.
Upon logging in, the user is immediately signed out again.
... repeat for every other session participant the user wants to log out of.
See: SLO: Okta