schemas
    pg_toast, pg_toast_temp_NNN

select relname, relfilenode from pg_class where oid = (
    select reltoastrelid from pg_class where relname = <tblname>
);
relname:      pg_toast_NNN
relfilenode:  <NNNN>

\d+ <tblname>
strategy
    * plain
    * main
    * extended
    * external
alter table <tblname> alter column <columnname> set storage <storagename>;

2023
https://habr.com/ru/company/postgrespro/blog/710104/