[dado3212]

I'm a big fan of sidenotes as a solution for this. If you're on desktop they'll pop out to the side and it's easy enough to glance over at them or stay focused on the main text without having to navigate around. On mobile that obviously doesn't work, but instead you can just have them open inline, so you don't have to deal with the annoying anchor link jump behavior and remembering where you were. And it's all doable with CSS and float, no Javascript!

Here's an example with a fair number of sidenotes:

https://blog.alexbeals.com/posts/possession

[jaffathecake]

It's ok, but you're still being taken out of the flow. Especially as the notes appear arbitrarily on the left or right. And yeah, you have to find your place again afterwards. It's way better than scrolling solutions though.

That particular example on mobile falls back to a revealing pattern, which is pretty good.

It still has the problem where it's just a test of your curiosity. You don't really know what the supplementary content covers until you expand it. The link text is just a superscript number which is kinda useless.

This is why I prefer the solutions in the article where the supplementary content has a heading that hints at the content.

[account42]

The entire point of footnotes is that they have been moved out of the main text because their presence would negatively impact the flow. If most readers are expected to want to read them then they should just be part of the text and probably not even in parentheses.

[rendaw]

Instead of using numbers, what about having a line from the text to the sidenote?