pkg-fallout@ complains about failing for qgis-3.16.0 in package[1]. It turns out, that I committed a pre-version of Makefile, which missed BUILD_DEPENDS=devel/opencl. Sorry for any inconvenience.
[1] http://beefy18.nyi.freebsd.org/data/head-amd64-default/p553574_s367123/logs/qgis-3.16.0.log