If I dare ask: re the various comments about approaches and the MCP speed window not being open...on the likes of the T7 once VNAV has gone into approach mode (triggered by any flap being selected and/or a couple of other parameters that escape me ATM) the MCP window will automatically be open, you have no choice in the matter, so you should certainly never end up flying a VNAV approach with the MCP window closed ...does the 78 use similar logic or is it even more mysterious than I imagine?
As for the HOLD FMA...as has been said to a simple soul it means the autothrust backdrive to the thrust levers is disconnected and therefore you can “hold” the thrust levers and manipulate them as required, if e.g you are descending in VNAV PTH, below the profile and the dozy machine hasn’t put any power on you can do it yourself.