I've bought a non-TTL Yongnuo flash (YN-560 IV) for my Canon 77D and it works fine when shooting through the viewfinder. However switching to Liveview mode, I found out that it annoyingly stops working. It is possible to get the flash to fire if I switch to high-speed burst mode, however in that case the flash fails to synchronize with the camera properly. Is there a way to force the camera to sync the manual flash properly?
I've read the answers to this related question, however my camera doesn't have a silent shooting mode, so they don't apply. Likewise the Canon manual says:
A non-Canon flash will not fire during Live View shooting.
However it obviously does if I switch to high-speed mode and the manual doesn't say anything about how to enable proper synchronization.