Not sure how advanced you are, but I used some combination of this: https://github.com/godotengine/godot/issues/6506
and in Project Settings > "General" tab > Display / Window:
... I set Size/Width to something like 160, and then Size/Test Width to a multiple of it - say, 480. (do the same with Height and Test Height.)
... and set Stretch/Mode to "viewport"
and finally: in the Import settings (it's a tab in the top-left corner) of any images you're using, you have to turn off the 'Filter' checkbox.
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Most of this I don't deal with anymore, I wrote a script to deal with it all for me. I stuck it in a pastebin if you're interested! https://pastebin.com/egH7N5gi
but basically it's just a lot of stuff like this, setting project settings through code:
ProjectSettings.set("display/window/size/width", width)
ProjectSettings.set("display/window/size/test_width", width * zoom)