I would be very surprised if a website autofocused almost anything on page load, except for very specific applications where that makes sense. I just tried clicking through some forms on gov.uk, which is a website that has spent a _lot_ of time testing and improving the UX of their forms, and none of them had autofocused elements, not even on later pages after having already filled in elements.

I can imagine screen readers would deal particularly poorly with this behaviour, because the user would be dropped in a field without any of the context of the page, just the field label to work with. However, I've not been able to test that out properly.

I don't think the behaviour you're describing is anywhere near as common as you think it is, and I suspect it would make a page less accessible for a number of kinds of users.

Sorry, missed the part about "form for data entry". If that's the main point of the given page, then sure, focus on the first input is fine.

Your original comment was to use tabindex to skip search, menu bars, breadcrumbs, etc. and for that there are better options.