Tip if you want to use Zigbee2MQTT is to checkout ITead Sonoff Zigbee 3.0 USB Dongle Plus based on Texas Instruments CC2652P (however note Z-Stack 3.x is not yet compatible with OH’s zigbee-binding):
Tip if you want to use OH’s zigbee-binding instead is to use a Silicon Labs based ERF32 based “Ember” (EZSP = EmberZNet Serial Protocol) adapter, preferably based on Silabs EFR32MG12 or EFR32MG21. Unfortunately, there is not much choice on the marked there today other than ELElabs ELU013 which is based on EFR32MG12 and also sold as Popp ZB-STICK 701554
https://elelabs.com/products/elelabs-usb-adapter.html
Alternatively if you want an inexpensive EFR32MG21 adapter and are willing to modify then check out:
Note that Silicon Labs EFR32 / EZSP based apter only have very early initial experimental support in Zigbee2MQTT and is not recommended to anyone other than developers of zigbee-herdsman.