MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
create table movies(id  Int,      title varchar(50),       genre varchar(50));
insert into movies select 1  ,       'return',     'Comedy';
insert into movies select 2   ,      'Scooby',     'Documentary';
insert into movies select 3    ,     'Halo'  ,     'Documentary';

Records: 1  Duplicates: 0  Warnings: 0

Records: 1  Duplicates: 0  Warnings: 0

Records: 1  Duplicates: 0  Warnings: 0

create table reviews (movide_id Int,  rating Int);
insert into reviews select  1  , 1;
insert into reviews select  1  , 3;
insert into reviews select  2  , 5;
insert into reviews select  2  , 5;
insert into reviews select  3  , 3;

Records: 1  Duplicates: 0  Warnings: 0

Records: 1  Duplicates: 0  Warnings: 0

Records: 1  Duplicates: 0  Warnings: 0

Records: 1  Duplicates: 0  Warnings: 0

Records: 1  Duplicates: 0  Warnings: 0

select genre, title, stars
from (
  select m.genre, m.title, stars,
  	Dense_Rank() over(partition by genre order by stars desc) rnk
  from movies m
  join (
  	select movide_id, Avg(rating) stars
  	from reviews
  	group by movide_id
  ) r on r.movide_id = m.id
)t
where rnk = 1
order by stars;

genre
title
stars

Comedy
return
2.0000

Documentary
Scooby
5.0000