Not receiving Updates on Xbox Series X

there are still no confirmed things, some games are announcing that if you buy it on xbox one in series x you will receive the game update for free

I don't know if these server problems are related to the updates they do for the game.

I remember not long after I installed the game on my Xbox series x last year it received an update a day or 2 later and I started getting a server error message on my Xbox series x yet on my Xbox one x the game played fine without an error message.

I would presume that if a game is Xbox One X Enhanced, those benefits will also appear when the game is played on Xbox Series X, along with any Optimized for Xbox Series X benefits that same game might receive through future updates. I doubt seriously it
would be a step backward when played on the superior hardware.

Keep in mind the Smart Delivery feature, which will enable Xbox Live to send the best possible version of the game to Xbox Series X automatically. So that may be the Xbox One X Enhanced version, or (if the developer makes such an update possible) the Optimized
for Xbox Series X version. Given the choice, I'd want the Optimized version.

Yes that is what was said in recent news however, it is still possible that these classic titles could receive a definitive edition update for Xbox One and Series X/S

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.