After the official announcement of RAD Studio 12.3 (including Delphi 12.3), I've done a number of posts on the Embarcadero blog site on specific new Delphi features introduced in 12.3:

Others at Embarcadero have also contributed, covering additional new Delphi features:

Some further blog posts are specific to C++Builder:

There are other features and many improvements added to Delphi 12.3. I'll put here again the links to the docwiki page covering what's new and the one with the list of bugs fixed.