Two servers, both running MariaDB 10.5.9. Server #1 has table:

create table foo ( x geometry );

Server #2 attempts to generate a federated table:

MariaDB [dalo]>   CREATE TABLE foo ENGINE="FEDERATED" CONNECTION='svr1/foo';

ERROR 1939 (HY000): Engine FEDERATED failed to discover table `svr1`.`foo` with 'CREATE TABLE `foo` (

  `x` geometry DEFAULT NULL

) CONNECTION='svr1/foo''

Originally found in a more complex table with multiple geometry columns. Only by removing these columns did the creation of the federated table succeed. Other tables without federated columns all work ok.

As far as I know there is no work-around for this.