In no particular order
1. Better naming. Xbox Series X/S is far too close to Xbox One S/X.
2. No Microsoft games on other consoles other than obvious stuff like Minecraft.
3. Don't worry about buying Bethesda and Activision-Blizzard and focus more on the quality of console and PC experience, a purer Xbox.
I suppose if they stopped simultaneous PC releases that could help, but there's virtually no chance they do that. To be fair, the acquisitions I mentioned for them to avoid probably would've happened too.

They could've probably sold as many Xbox Series consoles by the end as Xbox One, Xbox 360 would be nearly impossible to reach. 

1) Different name.
2) Abuse the purchasing power of Microsoft to buy up all the components during the early live shortage to get a head start.
3) Pay Square Enix to get Final Fantasy 7rm at launch, better yet exclusive
4) Accelerate game development for first parties, if not possible buy console exclusivity of big games (see FF7)
5) Less focus or no Gamepass, it devalued the brand.
6) Buy market share with game and hardware pricing vs. competition (Microsoft has the deep pockets to do it)

Now not in favour of big corp doing some of the above, but it would have worked.

Yeah they definitely should have been more hands-on with their developers rather than just letting them do whatever. They needed system sellers and they needed them in 2020-2022.

Halo Infinite and Starfield missed the mark. Both were still good games, but didn't come close to the hype. Forza Horizon is the only series to have hit it big this gen for Xbox. Grounded did better than expected given it was made by 13 people, but that is a smaller title and not a system seller. 

If things lineup Elder Scrolls 6 could be a launch title for Project Helix or come out the following holiday. Sure, the game will most certainly be cross-gen and playable on the Xbox Series. I am also fully expecting Halo 2 and 3 remakes, which given the new CEO will likely be Xbox/PC only. Only reason Halo remake and Fable are still coming to PS5 is due to those versions were already announced.

IMO Xbox needs to make every single-player focused game of theirs Xbox console exclusive. Even if we are talking timed exclusive. 

Apologies if any of these have been mentioned previously as I'm at work typing in a rush and haven't read through all the answers properly yet. But from my experience,

1) Make basic online free for players (Not game pass just access to online like PC)
2) Kept the backwards compatibility programme going throughout the whole of this generation although it's good to see it kind of coming back recently)
3) Refreshed the Series X to be a bit smaller - slimmer (around 2023/4) to be on par with PS5 Slim.
4) Refreshed the Series S around 2025 to have a disc drive but keep price the same (this would have complimented the backwards compatibility programme)
5) More integration with Steam, have options to see friends online/invite to cross play games direct through your Xbox for example (not discord).

6) Just make more games, a lot more games! Even indies!

7) Bring back Avatars, with options to buy/win cosmetics + customise them.

Things worth mentioning:

Xbox cloud services still back up your saved game data without any subscription. This is very generous considering both Nintendo and Sony charge for that service. I feel Xbox is a better platform than people recognise. Plus they kept controllers universal and the Series X is an excellent console and very reliable. The Series S is a really cool machine.

Xcloud and all the "Everything is an xbox" did really bad to xbox series.
Also, their core games on PS5. Even their games wanted to get money from PS5 owners... (consequence of gamepass and the new culture of not buing games, specially at day 1, when the most revenue would come).

Is kinda they chose to not sell as many xboxes, and get cash from services or PS5 instead.
Xbox could get more shipped units, but with worst global revenue.

Yeah the whole "this is an Xbox" campaign remains one of the worst pieces of advertising I've ever seen.

"Hey guys, you know the product we make and sell? Well guess what, you don't need it, so why buy one?"