I keep hearing people say this, but I haven’t found it so: in over a decade, I think I’ve only seen it twice. Looking through my password safe which I’ve been using for about twelve years with over 200 entries, I have nine cases with multiple origin URLs, and most of them I’m confident I added manually because I didn’t like the URL it recorded automatically (e.g. it’s on a different domain from the main site, and the specific path is for signup only, but I want to be able to “visit site” from the password safe and get to the login page or at least the homepage). I think that only two of them have ever actually used more than one origin: a banking one that switched from .com.au to .com at some point as part of a broader global restructuring (and they made a fair bit of noise about it, and you had to partly make a new account anyway), and a Microsoft account. There’s a third that I can’t check (COVID-related, gone) that might have been, but I don’t think so.

Now on a few occasions I’ve had to copy passwords in order to access things in a different browser, and I think I did encounter one site some years ago where autofill didn’t work, but I really do find autofill almost completely reliable.