I think this is dependent on reading strategy, which is dependent on cognitive style. For someone who skims a lot, they are frequently making active decisions about what to read while reading, so they're skilled at this and not bothered by footnotes. I love footnotes. This style may be more characteristic of a fast-attention cognitive style (and ADHD-spectrum loosely defined).

For those I like to refer to as attention surplus disorder :) who do not skim much, I can see the problem.

One strategy is to simply not read any footnotes on your first pass. Footnotes are supposed to be optional to understanding the series of ideas in the writing. Then, if you're intterested enough to get further into details, you go back and read some or all of the footnotes.

I agree that we could use footnotes better by either using them one way and stating it, or providing a brief cue to how it's used in the text.

I strongly disagree that footnotes as classically used are not useful. And having any sort of hypertext improves the situation.

Footnotes are usually used to mean "here are some more thoughts/facts/claims related to those you just read before the footnote mark". Sometimes those will be in a whole different reference. After you glance at a couple, you know how this author is using them.

Appropriate use of footnotes is part of good writing. As such, it's dependent on the topic, the author, the reader, and their goals in writing/reading. And thus very much a matter of individual taste and opinion.

Endnotes of varied use, without two-way hypertext links, on the other hand, should die in a fire.

So, if you wonder whether you'd care for the content of a note, you have to look at the note, switching to the bottom of the page and breaking your focus. Thus the notion that footnotes are optional is an illusion.

I agree with this. Too many footnotes can really slow readers down when they have to check each for whether it's relevant.

Similar points apply to adding too many unnecessary links. Specifically links where it isn't clear where they lead and what point is made in the link target, as in the previous sentence. (Do they provide a citation? Important additional explanation? Just an allusion to some related idea? So the same issue you point out for footnotes.) Like footnotes, many such links should probably be left out entirely, because they add too little value compared to the amount of reading disruption they add.

For other links, it should be made clear in the text what their purpose is or where they lead, unlike in the example sentence above. So that people can safely ignore them if they don't need them.

Moreover, links to (e.g.) Wikipedia, which explain a simple concept, can often be sufficiently replaced with a short one line explanation inside the main text, perhaps in parentheses. This doesn't require readers to engage with a whole new webpage which likely contains way more information than necessary.

Footnotes are good in translated works. I read the 3-body trilogy translated into English, and it was very helpful to have notes from the translator explaining certain points of cultural context that a Chinese reader would be expected to be familiar with.