This seems to be resolved for me on Xbox with 1.21.30.
Its simply a workaround, it is not a solution, but it may help identify the true issue to help in debugging and eventually a real solution.
Even though you may have the banner that states:
You have disabled Multiplayer in Xbox Account Settings. Learn More
You still have to go to the Multiplayer tab and disable the radio button. Then the CREATE button will be green and clickable and you can now create your new world. Somewhere between 1.21.2 and 1.21.21 this changed and now must be done for each create operation.
Can confirm that in 1.21.21 when you attempt to create a new world, even without any other changes, the create world button is not green and is not selectable. All other tabs and adjustments will work but you can not create the world in the end.
I do not require the complex steps to reproduce, I only have to exit the boat with either the A or the B, and the boat will disappear. Yes, you can not enter it again if you happen to find the space it occupies, but saving and reentering the world does make it visible again. Interesting though, even if you do not collide with it, it does not always appear in the same space that it was exited from, sometimes multiple blocks away. Happening more with 1.17.40+ updates. Xbox version, no experiments, no unlocks, simply survival mode.
This is broken again in 1.21.44, you have to disable the mutliplayer option to get the CREATE button to go green so you can create a new world in single player mode.