Each default theme (those that are included with new WordPress versions) is an entirely new theme. There has been a new theme for nearly every year since 2010 with a corresponding theme name for the year. Twenty Twenty-Three is simply the latest of these themes. The goal would be to use the theme as a starting point rather than to attempt to make it similar to a previous theme.
If you wish to try out a new theme without affecting your live website I’d recommend creating a separate WordPress installation for testing. You can sometimes create an additional site with your host but there are also simple ways to create a Local WordPress installation that would be run from your local computer. Here are a couple of options for that if you are interested. https://github.com/10up/wp-local-docker-v2
The first is more complex to set up and geared toward developers, and the second is much less complex to get going for most people.
Thank you Daisy, I was expecting an addition. But I now understand how it was thought by WP. I can now proceed with TT2. By the way, I haven’t found anyone in my area who does anything with Gutenberg etc. Unfortunately.
You’re very welcome! I’ll mark this thread as resolved but feel free to start a new one if you have any other questions.