Not all phones use/used RNDIS to tether its internet connection, some like mine use cdc-ether or cdc-acm, plus there is bluetooth tethering as well as just plai

Not all phones use/used RNDIS to tether its internet connection, some like mine use cdc-ether or cdc-acm, plus there is bluetooth tethering as well as just plain NAT'ing an ethernet adapter plugged into the phone. If you're in a desperate situation where RNDIS does get removed from the kernel but you still need it, I'm guessing there may either be out-of-tree modules you could build, or if all else fails, you could run a VM with an older kernel.