Logical replication on two identical databases but diff versions

Hi,

i have two db servers pg12 and pg14 and they have exactly the same data in
all schemas and tables. I tried linking both by setting wal_level=logical
and make pg12 publisher and pg14 subscriber (with copy_data = false,
create_slot = false, enabled = false)
Then i created a logical replication slot on pg12 and enabled subscription
and logical replication was running just fine and all changes from pg12
going to pg14...
Is this expected ? I did not play with any of advancing of lsn anywhere...

If this is expected, that means i can have a pg12 cluster of primary and
replica ... then i can take the replica out of cluster , make it writable
using pg_promote and then pg_upgrade it to pg14 and then link it like above
to old pg12 via logical replication...and then slowly after ensuring no
issues, phase out pg12 and replace it with pg14, no downtime upgrade ?

Is this correct? (Of course no schema changes while this is being done) and
i set max_wal_size to a large value to retain enough wals.