Which version of qemu and glxgears do you use?
Tested with qemu-4.2 and qemu-5.0 and debian/sid mesa-utils-8.4.0-1+b1 and it works fine.
Which version of qemu and glxgears do you use?
Tested with qemu-4.2 and qemu-5.0 and debian/sid mesa-utils- 8.4.0-1+ b1 and it works fine.