Greetings @ldvp,
In general HDMI resolution and display timings are gathered from the EDID information given by that specific display. Meaning that the resolutions available are given by the display itself.
The way you’re trying to change the resolution via the weston.ini is a correct way to do things. We even document this here: Display Output, Resolution and Timings (Linux) | Toradex Developer Center
But, I believe unless the mode is actually defined via the EDID then it probably won’t work. So the first question would be to determine if your HDMI display supports the resolution you’re aiming for. You can determine this with a display utility like xrandr or fbset. These utilities should list all the available modes for the connected display.
In the case the resolution you want is not provided by your display’s EDID, you do have an alternative. You can inject an alternative EDID with the resolution you want: Display Output, Resolution and Timings (Linux) | Toradex Developer Center
Though please note there may be unintended effects from forcing an EDID that did not come from the display.
Best Regards,
Jeremias