Although developers said you can use doors to explore underwater caves, however this does not work in bedrock edition. If they rejected to change it in java edition, then I suggest to remove doors from shipwrecks, or change it in bedrock.
Source: https://www.youtube.com/watch?v=TycBrFKEteU at 43:20.
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Thank you for your report!
We're tracking this issue in MCPE-35481, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
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Duplicate of MCPE-35481, The doors are waterlog, WAI.