Hi,
Thats because you starting following the instructions *after* upgrading, not
before.
You need to reinstall macports over the top of your current installation, to
update to the binary to that for your current system, then try again.
https://www.macports.org/install.php
Following the instructions of migrating macports is a dead end to me right now.
all attempts to uninstall or do anything woth the port command ends with that:
kuku@Christophs-MBP ~ % port -qv installed >myports.txt
Error: Current platform "darwin 19" does not match expected platform "darwin 18"