I’ve tested this for you and could start TV and AVR by CEC if I let wake them when the mediacenter screensaver deactivates, for this I
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configured the screensaver at settings->interface->screensaver (I used Dim and 1 minute)
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configured CEC at settings->system->input->peripherals->CEC adapter, see picture attached
(Hint: The Connected to HDMI device menu item only is shown if you first reset this CEC config to Defaults; if this is not set correctly, it does not work, here)
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restarted mediacenter/Vero4k and then disabled+enabled HDMI control/CEC on AVR and TV, so they can “learn” the situation
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if the screensaver is active and TV and AVR are in standby, a single press to any button on the Vero4k remote control wakes up TV+AVR (at least in my environment)
Since the various CEC-“dialects” and proprietary implementations, you can only try whether this is from help with your environment.