Errata patches for libX11 have been released for OpenBSD 6.6 and 6.7. The recent security errata broke X11 input methods.
Binary updates for the amd64, i386, and arm64 platforms are available via the syspatch utility. Source code patches can be found on the respective errata page: https://www.openbsd.org/errata66.html https://www.openbsd.org/errata67.html