I was trying to make an addon that allows the player to go through walls just like in java edition spectator mode, but even with zero collision box and having this:

"minecraft:physics": {
"has_gravity": true,
"has_collision": false
}

in the player behavior (player.json), I still can't go through walls. I could go just partially inside a wall because I had a collison box of zero dimensions but I could not go through even a 1 block thick wall. I can also walk normally on the ground.

I made a quick pack for you to test the bug yourself. Add this pack to a world then type in chat: (make sure cheats are enabled)

/event entity @s minecraft:spectatorm

You will get a tiny collision box that allows you to clip inside blocks but not go fully through them.

You can return to the normal player by typing:

/event entity @s minecraft:base_player

This is really frustrating because it killed the hype I had for having spectator like features in Minecraft Bedrock.