Hello,
As per error it seems you have initiated source data with PG13 binaries.
Could you please connect to both source and target psql and share out of select versions();
Also share pg_upgrade complete command which you are using.
Regards,
Abdul Sayeed
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Sunday, 19 March 2023 at 11:29 AM +0530 from david.g.johnston@gmail.com <david.g.johnston@gmail.com>: