Installing latest Vagrant 2.2.19 and VirtualBox 6.1.28 seems to have resolved this issue (at least for me). See Vagrant 2.2.18, OSX 11.6 cannot create private network - #22 by robert914
Installing latest Vagrant 2.2.19 and VirtualBox 6.1.28 seems to have resolved this issue (at least for me). See Vagrant 2.2.18, OSX 11.6 cannot create private network - #22 by robert914