Your questions show you have not taken the time to learn about 'changing domains' - or about 'duplicate content'. Info about moving or changing domains has been posted here many times and will be helpful to you.

Use the advanced forum search to find POSTS with the keywords

change domain

or

switch domain

and read/learn before you make the move.

Then if you have specific questions, ask them here.

I think you should keep your current domain as it is and add new fresh content on the new.

If you switch, you might lose your rankings.

I take it you're rebranding. You should redirect the old site to the new URL. One thing I have learned through the years is the importance of the domain name. It is always cheaper and less time consuming if you start with a domain name that you are 100% satisfied with. Good luck.

switching domains works, I did already.
you might loose few weeks.... ranking.
move content, keep url structure.

redirect old domain to new domain with 301 redirect.
make sure in htaccess you permanent redirect old URL to new URL.

I see this very often with our clients, they buy with us a new domain , a new gTLD. Because they believe it is upgrading their branding.

If it is done well, your ranking is positive impacted for example if your new domain is an exact match of your main keyword. but it can turn also bad if your domain is NOT supporting your SEO.