This thread has to many different things mentioned. What exact system is in use today, the exact problem today, what did user do before the problem occurred? I do not mean to be rude but I have time problems, not enough of it.
If I understand correctly this problem happened after user upgraded an existing working ROME X11 X86_64 system? And user has since reinstalled and still has the issue? I saw iso #4119 mentioned. The most recent ROME Plasma6 X11 x86_64 is #4305.
In other words we need to simply to where we are right now not days ago.
Some general info about the ROME upgrade Nov.9 is here. This is basically the upgrade from plasma6-sddm* to sddm* after which you have to re-enable systemd sddm service like this:
systemctl enable sddm
To be sure it is enabled:
systemctl status sddm
reboot
If you have the correct packages installed and sddm is working and there is some problem I may not be the best person to help, if so we can get other people involved. But we would need logs to do anything. I believe I described the journal logs needed here. I do not see any journal log posted, did I miss it? It needs to be a log from a boot failure on the problem system. If other logs are needed we will advise.
There are a number of other possible problems but without logs we can only speculate.