Establishing SPI between XIAO nrf52840 and Arduino nano

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#42 
(SCK)D13 --- HV1 LV1 --- D8(SCK)
(MISO)D12 --- HV2 | LV2 ---D10(MOSI) 
(MOSI)D11 --- HV3 | LV3 --- D9(MISO)
    (SS)D10 --- HV4 | LV4 --- D7(SS)
             5V --- HV5 | LV5 --- 3V3
        GND --- GND | GND --- GND

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#43

think of it like this

if this unit is the Master its is Out-- if it is the Slave it is In → MOSI AKA TX

or

if this unit is the Master its is In – if it is the Slave it is Out → MISO AKA RX

#44

This is my view.
I don’t think the nRF52840 is Slave in this situation. I checked the signal with a digital scope and it was working as Master.
You will have to find an SPI library for Slave or, if you can’t find one, build one yourself from scratch. Software skills are required.