Brushes cannot be made available in adventure mode by command

What do you mean is that you cannot give yourself a brush via give command, when cheats are enabled and the gamemode is set to adventure? Do you use command /give @s brush? 

Sorry for the incorrect description, the correct one is that you can't scrape the suspicious sand in adventure mode by clicking on it with the brush in your hand.

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However, this issue is Working as Intended.

The report you have submitted is working as intended:

This feature is consistent between Bedrock and Java Edition. .

Please note, that mechanics of the game may change between updates.
Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.

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