Bedrock edition works very different than Java Edition under the hood, this means just Geyser alone is not enough to make LEM playable on bedrock.
Many elements, such as the UI, Menus, and Game Mechanics (ladder climb speed, knockback, etc.) need to be accounted for before Bedrock can be fully playable.
Bedrock support is currently under development, however it is still very early and will likely take a while to be ready for use by everyone.
However, if you would like to play Battle with the first 3 maps right now, you can play Ultmate_Mario’s remake Here!