Minecraft version 1.18.2
Forge 40.2.4
createplus-1.18.2_v0.5.1a.jar

Player has helmet and create backtank, but oxygen keep depleting underwater

That is correct. On this version minecraftversion it didn't work. Unfortunately 1.18.2 is discontinued so I won't fix it. Sorry

Do it yourself instead if your really need it. I cant put up a patch if your fix it and set up a pull request

Lazy piece of shitbag

1.18.2 Backport is now available. Have fun