All of a sudden (I guess after upgrading lots of libs in archlinux) qtCreator's (at the moment 4.15) debugging stopped working. I tested with gdb manually. Symbols were there and everything looked(!) fine.
BUT not a single breakpoint was hit, and manully breaking ended up in the assembler-overview as if the debugger is not using symbols at all!?
After a lot of trying....I got debugging back, by setting the debugger actually to gdb (setting was LLDB).
Tools->Options->Kits. Select your kit (for me Desktop). Something like this will show up:
Choose /usr/bin/gdb
At least for me this did the trick.