And when I use a passphrase that my password manager generated, the sign up form called it “weak”.
Then respectfully it might be your fault, but I don't know the metrics for which Lemmy rate the passwords, you can also use this other estimator, download the local version of course:
https://github.com/dropbox/zxcvbn
I for instance used a simple setting:
and got:
;;75.cupcake.manly.argument.53%%
testing it on https://lowe.github.io/tryzxcvbn/
Lemmy although gives it a "medium" quality rating to the password, so I guess it must estimate it differently
"92 minutes of applauses"