Yeah, the status-quo for me for several years has been "I don't know" because most things I build end up needing to debug something I don't have an immediate answer for, or construct something new, or talk to a new team, or find a new lib, or change a new setting, or migrate to a new platform. If I'm repeating work I'd done many times before, that's something that should be made more flexible and automated so I don't need to do it any more. (these of course exist, but you're pretty easily replaceable if this is a super-majority of what you do daily)

So my estimates are pretty much always "if it's well-built, documented, and fits what I expect, a week or less. If not, up to 2 months or more, but I should know more in 2 weeks". Getting a more accurate estimate quite often means spending as much or more time investigating than it would take in the optimistic case, so usually the answer becomes "give it a shot and we'll decide again later". Sometimes I have good news, sometimes not.

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We sit on top of millions of lines of code, changing faster than we can read much less understand. You cannot know it all, nor is it worthwhile to try in the vast majority of cases. Poking into new territory is common, and the ability to do so effectively is a super important skill.