Problem with connected LG TV

Except my main monitor, i have connected my pc with a LG TV though HDMI.
When TV is open the log screen and generally the user interface appears with very very small letters.
I have installed Leap 15 but i had the same problem also with previous versions!
I cannot understand why it appears like that and how to change this.
Thank you in advance!

Which display manager are you using?

]/usr/sbin/update-alternatives --query default-displaymanager


ps -A|grep dm

If using sddm read the following regarding HiDPI displays…

I Recieve the following:

$> /usr/sbin/update-alternatives --query default-displaymanager
Name: default-displaymanager
Link: /usr/lib/X11/displaymanagers/default-displaymanager
Status: auto
Best: /usr/lib/X11/displaymanagers/sddm
Value: /usr/lib/X11/displaymanagers/sddm

Alternative: /usr/lib/X11/displaymanagers/console
Priority: 5

Alternative: /usr/lib/X11/displaymanagers/lightdm
Priority: 15

Alternative: /usr/lib/X11/displaymanagers/sddm
Priority: 25

Alternative: /usr/lib/X11/displaymanagers/xdm
Priority: 10
$> ps -A|grep dm
2363 ? 00:00:00 sddm
3169 ? 00:00:00 sddm-helper

Ok, so that confirms SDDM is in use. Did you follow the links given yet?

For the KDE desktop itself, this might be helpful…

What is the model number of your LG TV? Does it feature 4K?

Thank you all for your help! It worked.
Now i have a new problem. Photos are not appearing clear in GwenVIEW and other apps. They have big pixels!
In some other apps it for example okular there is no problem.
Could also be fixed?
Thank you in advance!

A quick search suggests that HiDPI support for Gwenview is being worked on. Not sure when we’re likely to see that implemented though.