Get unexpected "1300 (HY000): Invalid utf8mb4 character string: 'FF'" when using c1 LIKE X'FF"

mysql> create table t1(c1 char(20));

update t1 set c1 = 'b' where c1 like X'FF'Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1 values('a');

Query OK, 1 row affected (0.00 sec)

mysql> update t1 set c1 = 'b' where c1 like X'FF';

{color:#f6c342}

ERROR 1300 (HY000): Invalid utf8mb4 character string: 'FF'

{color}

set names 'utf8mb4';

drop table if exists t1;

create table t1(c1 char(20));

insert into t1 values('a');

update t1 set c1 = 'b' where c1 like X'FF';