Has you follow the instructions in https://maiconpinto.github.io/cakephp-adminlte-theme/start
I did it for cakephp 4 and worked fine.
To customize the layout https://github.com/maiconpinto/cakephp-adminlte-theme/wiki/Customize-Layout
and instead of src/Template/Plugin/AdminLTE/Element/.ctp
do templates/plugin/AdminLTE/element/.php