There is a big thread on changing the physical layer to 125 kbps and using the LongRange mode here
https://forum.arduino.cc/t/nano-33-ble-nrf52840-ble-long-range-pairing-mbed-ble-api-adafruit-lib/644684/10
I think the problem could be partly solved if both devices had external antenna
The Nano33 BLE has an antenna (unless the board is defective and is missing the 5 small components in green antenna) and most people can get more than a few meters range.
I think that the range issues are most likely on the Microchip RN4870 side.
Even if you set the nrf52840 to long range or the lower kbps how are you going to get the Microchip into the same mode?
I think the most promissing thing to explore is the rn4870 antenna.
http://ww1.microchip.com/downloads/en/DeviceDoc/50002489C.pdf
Some models are supposed to have an integrated antenna, and the data sheet says the ones without (rn4870u) can have one added.