Whenever I boot my computer I get the message
Oh no! Something has gone wrong.
A problem has occured and the system can't repair. Please contact a system administrator
Here is an image -

It happened after a restart !! BTW graphics and other drivers are up to date , I can still acesss tty and grub recovery
I have seen this similar question but it isn't helpful at all, it just says to update but don't tell how to solve this problem.
@matigo requested to tell that how I installed Xubuntu
So As I mentioned before, I just purged ubuntu desktop and installed Xubuntu
sudo apt --purge autoremove gnome*
sudo apt --purge autoremove ubuntu-desktop*
sudo apt --purge autoremove gdm3*
sudo apt install tassel
sudo tasksel install xubuntu-desktop
However after running these I could still see ubuntu on login screen but I wasn't able to log into it so I removed Ubuntu from -
/usr/share/xsessions
But however after sometime, I wanted ubuntu-desktop back on my sibling's request, So I tried to do
sudo tasksel install ubuntu-desktop
(I did this before rebooting the changes of xsessions directory) After this I rebooted the system and broke into the error
After that I tried reinstalling gdm3 and ubuntu-desktop, xubuntu desktop, several time, I tried to switch to lightdm too.
Edit-2
I did this command by chance
sudo apt install --reinstall lightdm && sudo dpkg-reconfigure lightdm
Now I am getting the login screen, but my desktop environments are still acting crazy

I don't know what is happening
If I choose Ubuntu or gnome or Xubuntu I get the same error "Oh no! Something has gone wrong....".
Only LXQT is working, reinstalling don't work even now please help me to restore Ubuntu desktop.
My system info:
OS: Xubuntu 21.10 Impish (It is Ubuntu only but I removed Ubuntu desktop and installed Xubuntu )
Kernel 5.13.0.21
RAM : 16 GB
Storage : 2TB only 67GB is used
CPU: Intel i9