I'm pretty sure if you use an simple XO - any you set it for EXT REF Clock it won't work.
And for sure you won't have the DCXO feature. There might also some other things I'm not aware of.
You should set it properly.
Maybe you should post this question better on the AD9361 forum here:
https://ez.analog.com/community/wide-band-rf-transceivers/design-support
Greetings,
Michael