You can go into blocks if you hit some combination of keys, like the attached picture shows....
This has happened a few times before, in previous versions newer than 1.16.
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osfanbuff63
Does MCPE-109925 describe your issue?
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MCPE-109925 is related, but not quite. This issue is without using an Elytra in creative mode from under a block. The attached picture shows my view when I'm inside the ceiling of the previous floor looking up.