We have problem that suggested (automatically generated) password when creating Share link does not meets password policy, mostly it is about password length (generated password has only 10 characters, our password policy requires more), and in at least one time I have seen generated password without upper case characters (our password policy requires upper and lower case characters).
It is somehow user unfriendly, that without correction of generated password (e.g. adding some characters manually) it ends in error.
Complex passwords for Nextcloud shares have no real security advantage. Highly complex passwords are really only important if the encrypted hash in the database or encrypted file (e.g. password database or encrypted ZIP file) is stolen and the hacker can hack at home or in an elastic cloud. With a Nextcloud share, this is completely irrelevant, since access is only possible via the application itself. And if the data within Nextcloud is stolen, the share’s password is useless anyway.
I hope you always transfer the password via a second way (not second email). If not, then the password is completely useless.
I think the better way is to create guests accounts with the app Guests. Then the password is a self service from the user and the guest user password (recipient) is always transferred with TLS/SSL and not with e.g. email or avian.