I had a similar black screen issue with the previous update. https://forum.manjaro.org/t/black-screen-with-mouse-pointer-after-login-window/181039
I use the Cinnamon edition, so lightdm not sddm but the symptoms appear to be the same? Like for you I’m not sure what I did that seemed to have fixed the issue. I now make it a point to first read the ‘Update announcement’ and all the issues others are having, and wait a week or 2 before applying the update. before updating, I also do a full image backup (using Rescuezilla) to an external hard drive - just in case!