Yeah, I see this repeated a lot but I haven't really noticed a difference. Maybe I'm just not picky on the topic. But my understanding was it was never traditional SD, but 720p.
Regardless, I use firefox and Amazon, Disney+, Netflix, HBO Max all work reliably for me. I believe there was a period were a couple of them didn't work for a month or two on linux when they came out but I wasn't subscribed to them then and they've always worked for me.
Quality on streaming services isn't good anyway, and depending on the exact hardware and devices you have connected you won't get "HD" on Windows, either.
Regardless, I use firefox and Amazon, Disney+, Netflix, HBO Max all work reliably for me. I believe there was a period were a couple of them didn't work for a month or two on linux when they came out but I wasn't subscribed to them then and they've always worked for me.