I have removed the quotation marks because strange characters appear in the copy to the SSH console from the web browser. If you see a black screen it is because the resolution is not supported by the TV, try another resolution. Resolution changes are permanent as long as you do not delete the disp_cap file (rm /storage/.kodi/userdata/disp_cap).
The command
echo 1080p50hz > /storage/.kodi/userdata/disp_cap | systemctl restart kodi
works and it is not necessary to restart CoreELEC and it is not necessary to leave the SSH session to try another resolution!