Hello, I am a Japanese plays tester for Game Freak, and I'm here to share some
of information about Crown Tundra DLC for you. (Sorry if my English is poor)

The DLC will be released in October, sometime in the middle of month. I do not know the exact date.

About 120 Pokemon will be added with it, some legendaries, new Galarian forms, and some new Pokemon.

The 2 new legendary titans in Japanese are called Regitricity and Regidrak, are electric type and dragon type. They will have shrines made for them in Temple of Ages, and will be able to catch after finishing story. There are rumors that they will be used to wake Regigigas in Sinnoh, but am unsure.

The gym leader from opposite game of yours will appear, so Melony in Sword and Gordie in Shield. You can battle.

There is not much story, you go around doing research missions like Pokemon GO, and that is how you discover things.

Hope this was easy to understand, it took my a long time to type, thank you!