Master mysq8 slave Mariadb 10.3 Error 22
The Master should not be a newer version than the Slave(s).  In this case, 8.0 has a lot of new collations that do not exist in 5.7.  And the defaults pull you toward them.

Plan A:  Change the collations in the Master.
Plan B:  Upgrade the Slave to 8.0.

Meanwhile, suggest filing a bug at bugs.mysql.com pointing out how awkward it is to upgrade a Master-Slave setup with 8.0 calling for a collation that does not exist in 5.7.