If you watch the popular streaming services on a Linux PC then you'll be lucky to get more than 720p and some only seem to provide SD anyway - even for content from the HD era. This despite obviously having access to more detailed versions that they'll serve you for the same money if you watch on one of their preferred platforms.

IME this becomes quite jarring if you're watching on a modern high-res screen - even something like a quarter-sized browser window or PIP on a 4K monitor - with other much sharper content visible nearby. If you're watching either full-screen or in a smaller window but without other more detailed visuals around it then personally I find it less jarring and I can still become immersed if the material itself is good. It's still noticeable if you're used to watching HD or 4K content on other devices but I'd rather watch something good in SD than not watch it. The same goes for old shows that were only made in SD originally.