The Bug:
You cannot drown in water cauldrons.
Steps to Reproduce:
Place down a cauldron and fill it with a bucket of water.
Place a trapdoor above the cauldron.
Stand inside of the water cauldron and close the trapdoor.
Take note as to whether or not you can drown in water cauldrons.
Observed Behavior:
You cannot drown in water cauldrons.
Expected Behavior:
You would be able to drown in water cauldrons.
Linked issues
Attachments
Comments

Can confirm in 21w03a.
Can confirm in 21w06a.
Can confirm in 1.16.5 and 21w10a. Video attached.

Can confirm in 1.17.1. Players drown in water cauldrons in Bedrock Edition (MCPE-105627); as this was fixed in the Nether Update, it could also be considered a valid parity issue. I am mistaken per the comment below.
@unknown
It is not true. In MCPE-105627, incomprehensible without the steps of reproduction and the expected result, what the author wanted 😞. + this report has never been confirmed.
I just tested the cauldron with water in version 1.17.40.21 and I don't even get bubbles. The category "Parity" should be deleted, because the behavior of the boiler in this situation is the same in bedrock.
I'd like to request ownership of this ticket since the current reporter has been inactive since May of 2019.

In 22w15a

Can confirm in 24w34a.

Confirmed myself in 1.21.3 and 24w46a, and also related, fish suffocate even you do get them inside the cauldron

Can confirmed in 24w46a.

Can confirm in 1.21.4 prerelease 3.

Affects 25w05a
This is similar to MC-126819 which was resolved as "Won't fix."