FileMaker Pro 15 user here. If you go to the support boards at FileMaker Community, they are afire with complaints and condemnations about this very thing. The latest (de facto) word from FileMaker is to not upgrade to Mojave. I'm reading an update for FileMaker Pro 17 is expected "sometime in 2019".
The most common issue people are encountering (with FileMaker 17, the latest release) is that imports from spreadsheets (Excel) are causing the software to hang, and that user-created buttons are either not working or not configuring properly.
My wife uses an app (Studio Organizer) for her karate school; it is a FileMaker-based solution. The author of that app sent out a terse email last month warning users about an inability to run the program if they upgrade to Mojave, the brick wall he's basically encountered in trying to solve the issue with Apple & FileMaker, and suggested that users strongly consider switching to a Windows-based computer if they want to continue to use the software.
What always strikes me -- infuriates me, really -- in these situations is how a one-man shop can use the betas and make sure his independent/shareware software app works with a new OS from day one of official release, and a huge software company (and one with direct ties to the OS mothership itself) -- with money & staff, one would think -- drags its feet and leaves users in the lurch.
This is especially infuriating in that there is no real alternative to FileMaker (database software) in the macOS world.
I've been using FileMaker since my first Mac -- a PowerBook 160 (running System 7.1). It was the first software package I purchased as a business. In many ways, the application is the same one I used back then (lots of things/set-ups are still the same as they were, and that's not necessarily a good thing; e.g., doesn't use the system's spelling dictionary). I wish they had some competition on the macOS, because it might keep them on their toes a bit more.
