Well in my case it was clearly time consuming as the update is not available through WSUS/MECM.
I imported manually KB5009608 to WSUS (with the almighty Internet Explorer, thanks to the activex control we still have to use to do that), then forced a sync of MECM (SCCM) so that it could recognize the update, then forced a check of the update on the servers, waited for them to report back to configuration manager (took about 1h i think?), then forced my Automatic Deployment Rule to execute, which downloaded and deployed the update to the appropriate collection.
I then forced another computer policy retrieval on the servers, which prompted the update to be waiting for installation, i proceeded, rebooted and voilà! :grinning_face_with_sweat:
On another server though it was deployed using WU without doing anything, so it was as easy as going to sconfig, and selecting "6" then "1". I have yet to use WAC in a broad scale, another thing on my growing todolist!
I guess if you don't have it showing up in WU/WAC, you can install it manually, by downloading it from catalog (it is indeed available there, i checked), then extracting the update cab from the msu file you downloaded, then copying the cab to the servers you want to update, then executing (cmd with admin rights) from the folder where your copied the cab :
dism /online /add-package /packagepath:Windows10.0-KB5009608-x64.cab
This should work!
