@HellGhostEvoX - Unfortunately, there is no way to disable the auto-creation of bulleted or numbered lists in Miro.
I have gotten used to pressing Ctrl/Cmd+Z immediately after pressing number+period which reverts the numbered list back to just “1.” – a two step process, but it works.
Wish List idea
If the disabling the auto-creation of bullets or numbered lists in Miro is a feature you would like to have, I’d recommend adding this as an Idea in the Wish List category by following the guidelines here: Wish List: Everything You Need to Know.
If you do create a Wish List Idea post, I would also recommend that you post a link to it back here, so that future readers of this post can quickly get to and vote for your Idea.