pip install Flask-AdminLTE3

from flask_adminlte3 import AdminLTE3

[...]

AdminLTE3(app)

from flask_admin.contrib.sqla import ModelView
from flask_admin.contrib.fileadmin import FileAdmin


class AdminLTEModelView(ModelView):
    list_template = 'flask-admin/model/list.html'
    create_template = 'flask-admin/model/create.html'
    edit_template = 'flask-admin/model/edit.html'
    details_template = 'flask-admin/model/details.html'

    create_modal_template = 'flask-admin/model/modals/create.html'
    edit_modal_template = 'flask-admin/model/modals/edit.html'
    details_modal_template = 'flask-admin/model/modals/details.html'


class AdminLTEFileAdmin(FileAdmin):
    list_template = 'flask-admin/file/list.html'

    upload_template = 'flask-admin/file/form.html'
    mkdir_template = 'flask-admin/file/form.html'
    rename_template = 'flask-admin/file/form.html'
    edit_template = 'flask-admin/file/form.html'

    upload_modal_template = 'flask-admin/file/modals/form.html'
    mkdir_modal_template = 'flask-admin/file/modals/form.html'
    rename_modal_template = 'flask-admin/file/modals/form.html'
    edit_modal_template = 'flask-admin/file/modals/form.html'


class MyAdminIndexView(AdminIndexView):
    @expose('/', methods=['GET', 'POST'])
    def index(self):
        return self.render('myadmin3/my_index.html')


from flask_admin import Admin
admin = Admin(name='Admin Dashboard',
            base_template='myadmin3/my_master.html',
            template_mode='bootstrap4',
            index_view=MyAdminIndexView())

{% extends 'flask-admin/base.html' %}
[...]

{% extends 'myadmin3/my_master.html' %}
[...]