Externally stored game forced onto Series X internal

Not really...

Xbox Series X games / upgrades / updates has to be installed onto the Series X internal or expansion card SSD,

You can have Xbox One games on your external hard drive that will get an Series X upgrade but the games will need to be transferred to the Series X and then the Series X upgrade will need to be downloaded onto the Series X SSD,

As an example...

I have Marvel Avengers on my external hard drive that will get the Series X upgrade and I will transfer the game over to the Series X SSD ready to download and update the game to the Series X version when available.

Games can be stored on external drives. No need to keep redownloading anything. Store Series X/S games on external drive and then transfer to internal drive when wanting to play.

You can use an external storage device for backwards compatible content and to store Series X games, but the Series X games will only run off the internal drive or the expansion card.

Yep.

Just plug the external drive into the series s or x & you're good to go.

If you want to play any games that have series s/x enhancements then that game would need to be stored on the internal drive or the external ssd you can buy.

If they're Series S/X games or enhanced games, they can only run on the internal hard drive or the Seagate expansion card made for the Series S/X. A regular external drive can be used to store the games if you're not playing them and store/play older games.