I’ve different scenario with you, but the main problem is the same. That I can’t go to Kubuntu desktop after booting, only TTY1 shows. I’ve been stuck for at least 4 hours and I’ve tried many solution, but with sudo apt install --reinstall sddm that I entered in TTY1 terminal, I can get my kubuntu desktop as usual like before. Thanks in advance for sharing the solution! 
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@Gabriel_Ronaldo:
Hi.
You´re welcome. I gather your problem is solved then. If there are any further questions, feel free to ask.
If I can´t help I´m sure there are lots of experts here who are happy to help out.
Greeings.
Rosika 