With these configurations in .env:
DEFAULT_REGISTRATION=approval
ALLOW_MAIL_NOTIFICATIONS=true
SMTP_* =

when a new user try to register they get an error message in the browser saying sending mail to admins failed.
in log file i find:
ERROR: [2ede51c2-818b-4155-ac0a-be0f5e9cbfc9] Support: Error in email delivery: PG::I
nvalidColumnReference: ERROR: for SELECT DISTINCT, ORDER BY expressions must appear
in select list
LINE 1: ...= $2 AND "role_permissions"."value" = $3 ORDER BY "roles"."p...
^
: SELECT DISTINCT "roles"."name" FROM "roles" LEFT OUTER JOIN "role_permissions" ON "
role_permissions"."role_id" = "roles"."id" WHERE "roles"."provider" = $1 AND "role_pe
rmissions"."name" = $2 AND "role_permissions"."value" = $3 ORDER BY "roles"."priority
" ASC