I need to relaunch th Wordepress website in German language

I would like to start a relaunch or switch to a new Wordpress News Theme, as we have a lot of old scripts and bugs on the old site that have been around since 2015 and we don't want to take that with us to the new site, only the articles and certain tools as well as ads that we need, what we have to consider when moving, preferably moving the 16,000 articles easily with and maintaining the domain structure, we do not want any penalties from google or the article cannot be found or any other negative effects. It is also important that we rank well in core Web vitals with the new page and that everything is clean. We are looking for someone experienced.

The website is in German language