Environment per About QGIS: QGIS version 3.21.0-Master QGIS code revision 8498c55 Qt version 5.15.2 Python version 3.9.5 GDAL/OGR version 3.3.2 PROJ version 8.1.1 EPSG Registry database version ...
QGIS 3.16.9 and 3.20.1 for macOS still not available for download qgis/QGIS-Mac-Packager#137 ...