Confirmed this happens to me too - also on iPhone and also with the iPad external “magic keyboard”
Using external keyboard, if you hit return to attempt to open a new block and then hit tab to attempt to indent that block, the previous block is also indented indicating that a new block was never opened and you’re just appending to the current block.
However, if you hit shift+return, then you apparently do open a new block because the newly typed text can be indented under the previous block or outdented to be same level.
The onscreen keyboard does not create a new block (return or shift+return).