We had PostgreSQL support, but we removed it. There were several problems, all of which having to do with the fact that PostgreSQL does not allow you to dump the structure of a table in a way that makes it fully reproducible on a new server. We did our best, but the dump could never be 100% complete, causing various issues in edge cases we could not catch – and there were some edge cases we could catch but not do anything about. Between that and the virtually non-existent support for PostgreSQL across third party Joomla! extensions there was no reason to continue supporting it.
Even if we supported PostgreSQL, you'd have to rebuild all of your sites FROM SCRATCH. There is no reasonable way to convert a site built on MySQL / MariaDB to use PostgreSQL, which is undoubtedly what you had in mind with your question. Therefore, you can't even transfer data; you will have to manually copy everything from the old MySQL-based site to the new PostgreSQL-based site, item by item, after rebuilding the site from scratch. Nobody will pay you to do that; that's building a new site from scratch, plus all of the associated data entry.
Moreover, as I explained above, the vast majority of third party extensions does not support PostgreSQL. This means that you'd have to rebuild your sites from scratch, without using third party extensions.
In my professional opinion, it is far less problematic and far more expedient moving your sites to a different host.
This might actually be a good idea anyway, since SiteGround has just told you and everyone else that they are not to be relied upon to provide a secure hosting environment. MySQL 5.7 is End of Life since October 25th, 2023 and no longer receives security updates. This makes it unfit for use in production, yet SiteGround has announced it will do exactly that for the foreseeable future!
Nicholas K. Dionysopoulos
Lead Developer and Director
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