during some test installation for a different application that shall work together with InvoicePlane I switched the database from mysql to postgres. The test scenario was mainly not for IP but for our other software, so I actually wanted to just setup IP as test application. During setup I realized that there is only mysql support during installation, yet I found drivers for different databases in the vendor directory. Also just playing around with some configurations within the php files did not yet bring the hoped switch to postgres.
As I found these drivers I guessed that database support for different drivers is somewhat planned but I am not sure how close the program right now is to just switching to a different database. It would be great to have at least some of the main databases supported, e.g. postgres.