How to connect a third-party database to Joomla?

Question

Joomla

There is a site on Joomla. It worked for some time, now there is an urgent need to transfer the database to an external server. Joomla swears, they say, it was not possible to connect to the entire configuration, in which localhost is not written, incl. and on 127.0.0.1. I checked iptables, it's not blocking. MYSQL server started, connected via DBeaver, MYSQL Workbench, telnet. Both machines are on the local network.

Answer 1

connected via DBeaver, MYSQL Workbench, telnet

And through phpMyAdmin, running on the same machine where Joomla, connected?
Look about JDatabaseDriver in the standard documentation https://docs.joomla.org/Connecting_to_an_external_...
On the hosting where Joomla is running, the driver must be available for the web server. And Joomla will be able to use any database if PHP is configured to support them. Databases work on a client-server basis, so there shouldn't be any difference between a remote and a local database.
I experimented with cluster hosting back in 2007, even then all PHP-based CMS worked fine.
Well, check the port, as it is written in the dock at the link above. It, if you need to specify anything, along with the host:'db.myhost.com:3307'