The TV will be connected with HDMI and computer will have its DisplayPort converted to HDMI by a supported adapter. But:

most adapters do not support the CEC Tunneling feature, and of those that do many did not actually connect the CEC pin. Unfortunately, this means that while a CEC device is created, it is actually all alone in the world and will never be able to see other CEC devices.

DisplayPort to HDMI Adapters with working CEC

HDMI-CEC Tunneling over DisplayPort | Arch Wiki

TL;DR

Connect your computer's DisplayPort with DP-HDMI adapter to TV's HDMI. To test if the adapter tunnels CEC, run in a terminal:

cec-ctl --playback && cec-ctl -S

Which should show at least two devices.