In my view, systems without an HDMI output or which default to a 4:3 aspect ratio are retro. But I don’t expect everyone else to share this opinion, and that’s totally fine. 🙂
PS2 defaults to 4:3, digital out can be things besides HDMI, and the vast majority of 360 consoles sold had HDMI out. If you want to draw the line elsewhere, no big, do your thing, there’s no one True answer to OP’s question… but your comment feels like whataboutism to me and adds nothing of value.
Fun to think that someday if USB C finishes to eradicate HDMI/DP they might become the sign that it is retro... Look at that! They had a dedicated plug for the video signal back then :)