MySQLi has its own set of login functions that you could use to replace the login page you use currently for MySQLi support. It would just be a matter of reapplying the two server behaviors for login as everything else associated with the login code should not be using the database. (of course the register and user update pages would have to be updated as well if you use them).
I could also help with this in an hour premier support ticket and show you how to do it.
The next version of DataBridge will be using an updated mail library. The error in that can be ignored and just turn off that warning. I could also correct it in a session it is really just a matter of renaming one or two functions, but that will still work in php7 they are just warning it might not in php8 and we will have an update out by then.