I think if you have recent (not sure how recent?) HDMI ports, you can do this via a HDMI cable, which you might already use for displaying purposes? Never encountered it myself until I recently got a PS5 and noticed it and the TV shared both control and power state, so turning on the TV turned on the PS5 before I disabled HDMI CEC.
Alternatively, maybe there are adapters for HDMI that could add/emulate it/something similar?
> The PulseEight USB-CEC adapter works by passively extending all the pins of the HDMI connector on from the "PC side" connector to the "TV side" connector, save for the CEC pin, which is intercepted. The data going through that pin is instead exposed over a USB serial interface to let a PC control and monitor CEC traffic
Edit: Ah, but that adapter wouldn't work for powering on the PC I suppose, I don't think USB has something like WoL.
In firmware interfaces you can configure whether USB and PCI-E devices can wake up the computer. Enabling USB wakeup made it possible on my machine, that I can wake it up by pressing any key on the keyboard.
Alternatively, maybe there are adapters for HDMI that could add/emulate it/something similar?