How do I duplicate items in Minecraft Bedrock creative mode?

how do i duplicate items in minecraft bedrock edition

You can place the items you want to copy inside of a chest or other block that can hold items. Then, use the 'Pick Block' keybind while holding Control at the same time to get that chest as an item and place the copied chest down to extract the copied contents.

Is this just my mouse

No, you can rebind the 'Pick Block' keybind to anything in the settings screen.

The 'Pick Block' key does not work to duplicate items on Bedrock edition in creative mode at the time of this writing (v1.16.201 on Windows 10).

However, duplication can still be done by duplicating a container.

1. Place a shulker box and load it up with items that you want to duplicate. This is nice for heavily enchanted items because it's a pain to place all those enchantments all over again for each item.
2. Break the shulker box and pick it up. Hovering over it will show a brief description of what's in it.
3. Now this same shulker box can be placed as many times as you'd like, it won't leave your inventory, effectively duplicating everything in it.
4. Note: Attempting to use the 'Pick Block' bound key on these placed shulkers will only pick an empty shulker box. You'll need to pick one up and continue from step 2 to continue duplicating the items within them.

If you go into settings, go to controller, then at the bottom select the empty square next to “pick block” and press a button to bind. If you press this while hovering over a block, you will get that block. You can even get spawn eggs by clicking a mob. However, you do not keep the blocks data. So it can’t copy items in a chest, text on signs, or commands in a command block.