When I built that command block elevator, the tutorial said that it was survival-friendly. But only in bedrock edition, because I tried it in java but the slabs just appear which is supposed to happen, but instead of lifting the player up, it suffocates the player. Clip coming out June 4-5. It works fine when the player is going down in the elevator.
========EDIT========
Clips released June 5, 2021 at 3:28 P.M.
Up function clip (Kills player) here Down function clip (Does not kill player) here
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It's not moving the block. It's replacing the blocks.
Unlike a redstone flying machine elevator, it's not pushing the blocks the player is standing on. Rather, the command blocks are replacing the blocks the player is standing on with air and will "move" the block. Move as in deleting one block and placing another block on top of it. That itself will not boost the player up, or at least not in Java Edition. (You said it worked in Bedrock).
To my knowledge, for it to work you have to be JUMPING, so that the command block doesn't summon the block at HEAD level, which is causing you to suffocate.
The ONLY reason why it works moving DOWN is because of GRAVITY.
What kind of tutorial was this anyways?
Also I can add attachments to others' posts? Jira? Mojang? See if noonshot2.png is in the attachments.
Please provide some screenshots or videos of this issue occurring whilst the F3 debug screen is enabled.