Wildcard forward all posts and pages with few exceptions

I want to move my domain from example.com to example.dev and also set a wildcard forward. I use WordPress for blogging, now I want all posts and pages to be moved to the new address but I want some pages to remain accessible with my previous address. For example:

I want both URLs to be used on a same WordPress installation, but some URLs (posts and pages) should be previewed on one domain and some on another and some on both, as explained.

If there’s a way to give posts and some pages URL of domain 2 and give the rest domain 1 it would be awesome. Like, instead of forwarding pages and posts, just rewriting their URL. For example, all posts now are on domain example.dev by default but also listed on example.com.

I don’t know how to explain this exactly.

Here’s my current .htaccess file:

A huge thanks and shoutout to Mr. White for the great answer and help. Thanks a lot.