How to re-produce:
Find an ocean
Start swimming like normal
Swim up to the surface but try not to let your player model switch from the swimming animation to the walking animation.
When you're just above the surface but your player model is still shows the swimming animation, repeatedly spam the jump button on the controller.
This will trigger the glitch and you will be able to swim at full speed without losing oxygen.
If you need help reproducing the error, watch my video in the attachments section.
Can confirm on Xbox & Switch 1.21.50
I will upload the footage soon.
You cant - it permently stays on mojang's servers until it is reached.
How to re-produce:
Find an ocean
Start swimming like normal
Swim up to the surface but try not to let your player model switch from the swimming animation to the walking animation.
When you're just above the surface but your player model is still shows the swimming animation, repeatedly spam the jump button on the controller.
This will trigger the glitch and you will be able to swim at full speed without losing oxygen.
If you need help reproducing the error, watch my video in the attachments section.