If a player creates a new world without cheats, they can play Minecraft in survival with achievements earnable. But players can abuse the system by doing the following:

1.  Create a new world that has achievements earnable.

2.  After creating the world, close it.

3. Open a game editor, such as Universal Minecraft editor, etc.

4. In the editor, select the world that was created with achievements.

5. On the editor, select the player(s) that are gonna get this cheat.

6. Through the editor, set the player(s) gamemode to creative.

7. Save.

8. Re-enter the world, and the selected player(s) will be in creative with achievements earnable.

With this, players can earn achievements in creative which is not allowed for Bedrock.