If you type numbered items like the photo above, OneNote will read it as "one dot" instead of simply "one". Although not a big deal, listening to the digital reader repeat "dot" over and over can be a bit distracting. While a future update may address this issue, the easy fix for now is to simply type your number sequencing differently.
Instead of typing a period after 1, type a parentheses or a minus. The application will still maintain automatic numbering when you hit the enter key, so all that's really different is the visual aspect of your text. Either of these alternatives will simply be read as just the number in OneNote's Immersive Reader, sounding the same as the way a real person would read it aloud. Try it and see for yourself.