Hi @Renginys check you have the latest firmware on the Samsung support site,if not can be downloaded to USB. However latest update is 2010.0 from 2020. https://www.samsung.com/uk/support/model/UE46ES6100WXTK/ Try the following settings, Home -Settings > General- Power and Energy Saving, advisable to disable Brightness Optimisation, Brightness Reduction and Motion Lighting. applicable. If all fine or still issue there . Can you check all cables and connections to ensure everything is secure. If so press and hold in Power Button for 5 seconds or so to reboot until you see the Samsung logo. If does not solve the issue unplug at mains for around 5 minutes, you could also try a Factory Reset. If still flicker after troubleshooting do a Picture Test, Settings-support_ Self Diagnosis- Picture Test.
If tests fail you would need to get in touch with Samsung Support for Advice,however this a 2012 model and repair options may well be limited. Generally Tv's will encounter issues at this stage.
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 5.0,Android 13 .