OK, let's try to do this step by step.

First, try this script:

use utf8;
binmode STDOUT, ':encoding(UTF-8)';
print "Séan\n"
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Does this work fine? If yes, as the next step, use the first two lines as the preamble for all of the following scripts.

Try to read the string "Séan" from the database base after you have inserted it via the mysql command line client. Does that work?

Then insert that string (as a literal, ie stored directly in the text file) into the database, and read it from the DB via the mysql command line. Does that work?

If any of those does not work, please copy&paste the output here, even if it contains "weird" characters.

If all of these work, you should also be able to round-trip the characters via perl+DBI.