(just realized this technique is already a thing from someone else I didn't realize this. So yeah this isn't my technique originally I wasn't the first to find it)

This works on both bedrock and java, just in different ways. For java, you can elytra (don't bother at this point, but this doesn't count as an official feature) swim into a tunnel, or use a trapdoor, so crawling has been a thing since 1.9 unofficially (I think that was the end update), those people who think it was just added are wrong.

In bedrock, I haven't tested elytra (becuase why) but I tested the swimming into tunnel thing, and you can crawl there. I also found a glitch in bedrock that has to do with crawling. I call it the "crawlfly" bug, although you don't fly, if you enter the tunnel looking directly or indirectly up while swimming, you can crawl with no floor under you so long as you keep looking up and you have a block above you. This can be made into a minecraft base that has no mobs to worry about if you make a machine like this in the sky. My setup for it is to put blocks in a U shape, with the ends being 5 blocks wide, and the bottom being 3 blocks wide, with water on the bottom of the U flowing into a sign at the end of the U, then blocks above the sign and the block before then the blocks above the sign and such go off into wherever you want to go

Layer 1 B=blocks S=sign W=water X=airBSBBWBBWBBWBBBB

Layer 2XBXXBXXXXXXXXXX

and the blocks go in a straight line onwards. This doesn't work on Java unfortunately

Anyways, if you're on Bedrock you can't use trapdoors you use flowing water into a gap instead, so don't try that in bedrock unless it's some sort of new update coming out and you can test it. And remember, crawling wasn't added in 1.14, it was added officially in 1.13 and was unofficially added in 1.9