Unbelievable how frustrating it is, almost on par with autocorrect correcting the same word twice after I typed it out twice.
I mean for ducks - I mean ducks, no ducks sake…
Once autocorrect decides a word is capitalized, the keyboard will always do exactly the wrong thing when you try to fix it. You’ll backspace to the first letter, and the shift key will highlight so you capitalize some non-capital word. Or, having been burned by this, you’ll tap shift to turn that off, but it guessed you would do that, so you’re still capitalizing. And if autocorrect changed a name to a common word, good luck capitalizing the name.
There is a PhD, and possibly a new branch of physics, to be had here.
I recalled Windows can do it by using Ctrl+Shift+V which paste without formatting. Just a extra key to make it happen.
[1] https://support.apple.com/en-qa/guide/mac-help/mchlp2299/mac