I've done more testing and the command isn't behaving properly.
if I only do --start-server-load-scenario SCENARIONAME, it wont start because it doesn't have a map to use. Makes sense.
--start-server FILE --start-server-load-scenario SCENARIONAME it will load the save i specify (must be full path), but it does not load the scenario into the server. When I close the server, it will save in the saves folder, but still no scenario.
--start-server-load-latest --start-server-load-scenario SCENARIONAME it seems to load the latest save file in the configured server/saves folder (like it should), but does not notify it did so. The Scenario DOES start, and autosaves add the scenario to the save file. But when I close the server (ctrl+c) it says it's saving to SteamApps\common\Factorio\bin\x64 (which fails)
So it half works...I can start scenario's from the command line into any new map i want. But closing the server has a bug which doesn't save the file properly. So progress is lost back to the last autosave.134.082 Info MainLoop.cpp:199: Saving map as E:\SteamLibrary\SteamApps\common\Factorio\bin\x64
Can a dev check this? definitely a bug.