Some USB zigbee dongles can be flashed to be "multi-PAN", but my experience is it's currently buggy and I would let them bake that for a bit longer.
Alternatively, both Sonoff and Home Assistant do a thread dongle for about $30 that you can use simultaneously with a zigbee one. Plus if you have any of the following, they can be used as a Thread border router: Apple TV, HomePod, Echo G4, Eero 6/7, Nest Hub, Nest Wifi, Google TV Streamer. There's also the OpenThread Border Router which can be used on certain ESP32 hardware (ESP32-S3 for $10 or ESP32-H2 for $6?) but that obviously requires more work.
Alternatively, both Sonoff and Home Assistant do a thread dongle for about $30 that you can use simultaneously with a zigbee one. Plus if you have any of the following, they can be used as a Thread border router: Apple TV, HomePod, Echo G4, Eero 6/7, Nest Hub, Nest Wifi, Google TV Streamer. There's also the OpenThread Border Router which can be used on certain ESP32 hardware (ESP32-S3 for $10 or ESP32-H2 for $6?) but that obviously requires more work.