You have to either postulate randomness or describe how it arises from determinism. I don't see any other logical possibility.

BTW, see this:

https://arxiv.org/abs/quant-ph/9906015

for a valiant effort to extract randomness from determinism, and this:

https://blog.rongarret.info/2019/07/the-trouble-with-many-wo...

for my critique.