If I understand correctly, the end effect is similar to disabling all subscriptions. Why not just add ALTER SUBSCRIPTION ... DISABLE for all subscriptions in the failover work flow? Migration of logical replication slots docs says so - https://www.postgresql.org/docs/18/logical-replication-upgrade.html.
The scenarios I am talking in this case are no major version upgrade, but PITR and Standby promotion cases.
Server is in read only mode (catalog cannot be updated) before promotion and subscriptions cannot be disabled.
-- Bharath Rupireddy PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com