5.7 is fully supported. Where does it say so otherwise?
In your guide, Setting up MySQL.
Also, I wanted to mention that I could not get Razuna 1.9.6 to work with MariaDB 10.1 or 10.3, no matter what I tried. I know that you have never said it would, or ever advertised that MariaDB was supported, but I wanted to try regardless since we are primarily MariaDB users here. I have no issue with the requirement for MySQL, it’s easy enough to set up MySQL 5.7 on a separate dedicated server, but I just wanted to mention it here for any other users intending on using MariaDB and finding it not working. (The folder tree never loaded, the animated “loading” graphic kept spinning without result, and the log registered an error.)