Paul,
QRecall is, for the most part, compatible with Mojave. There are still issues with Full Disk Access, which we're currently working with Apple to resolve, but you've taken the correct step of adding the ~/Library/Application Support/QRecall/QRecallHelper program to the Full Disk Access group.
There are some minor bugs you might encounter. Mojave makes some subtle changes in how timers work and you might experience issues like the QRecall scheduler sometimes won't actually schedule anything for about 15 minutes after you first boot the system?oddities like that.
Mojave doesn't really change how the archives are accessed, so if you're getting "waiting for archive" status messages then maybe something else is going on. You might start by sending us a diagnostic report (Help > Send Report) and take a look at the troubleshooting topic in
Help > QRecall Help > Guide > Troubleshooting > Problems > Can't Open Archive. (Note that opening an archive to modify it and opening an archive to read/browse it are different modes, and one can still work while the other is stuck.) Often just waiting 10 or 15 minutes, or a restart, will break these kinds of deadlocks.
The big outstanding issue is that Mojave's Full Disk Access doesn't act consistently. Even if you grant the QRecallHelper program Full Disk Access, some future captures might still be unable to read restricted items. Keep an eye out for an update that addresses this.