Per le versioni precedenti alla 8.0...
SELECT *
FROM
( SELECT a.*
, @i := @i+1 i
FROM my_table a
JOIN (SELECT @i:=0) vars
ORDER
BY highscore DESC
, userid
) x
WHERE name = 'jennie'
OR i <= 3
ORDER
BY i;
https://www.db-fiddle.com/f/hYsiCE1bXeTnR2HzoJkKiR/0