Great, gdb no longer works on my MacBook:
(gdb) b main
Breakpoint 1 at 0x100000654: file main.c, line 46.
(gdb) r
❌️ Don't know how to run. Try "help target".
However, lldb works fine. Moreover, it looks like I now need to compile with
clang to generate proper debug symbols (clang -gdwarf-4 (...)). Related issue
on GH. Sadly, lldb is not supported by termdebug in Neovim.