@rustykenMisspelling and grammar errors seem to more relevant since the 1990's. Before then there were almost no online amateur authors (except some fan fiction, slash, and such on some BBS networks. Self-Published books were rare. There were some "Fanzines" and other printed works, but even those seemed to have competent editors or at least proofreaders. Quality of content in the last two decades seems to be better, IMHO.
I can only recall a very few such errors in books I read K-12, and those mostly in textbooks. Heinlein, Hemingway, or the Hardy Boys, there were no such errors I can recall. I noticed such things back then too. I averaged 96% to 99% reading comprehension on numerous tests, and that included noticing errors in the text.
Perhaps now that I have learned better how to self-edit, and have read a dozen or more books, and taken several college writing classes, I might be a bit more aware of such things. However, I still read some 200 pages a day (on average), for research and entertainment. I notice errors are present in nearly all books written after the mid-90's and almost totally absent in older books.
I believe that using word processors, and also "spell-check" programs have caused nearly everyone to "skim" and often see what they expect. There is also a tendency to over-rely upon our programs to catch most errors.
I am more likely to notice errors in another person's writing. Knowing what I intend, as well as having read, re-read, and re-read etc. so often my own writing, I (and many others just don't "see" the errors in our own writing.
Sometimes such errors bother me. Sometimes I make note of the errors, and then PM the author urging corrections. I have a volunteer proofreader, and yet both of us will miss 3 to 6 errors per 10k to 15k words per chapter.
I try to read what I post within 48 hours after posting. I write on a laptop, however, due to circumstances, I often read (and post in the forums) using my phone. Formatting, type, and layout of the paragraphs are different on SOL than they are on my laptop using LibreOffice.
I try to note down the errors on scratch paper, then PM the author. I do the some for my own writing.