RDS MySQL 8.0.16 has empty "INFORMATION_SCHEMA.ST_SPATIAL_REFERENCE_SYSTEMS" table
The new MySQL v8.0.16 image on RDS (as of writing this) is missing spatial references other than SRID 0. 

As a workaround, you can create a new instance with v8.0.15 and then perform the minor upgrade (requires reboot).

select count(*) from INFORMATION_SCHEMA.ST_SPATIAL_REFERENCE_SYSTEMS


...returns:

 5152