The belief that some things just happen. No one is at fault and there is no cause. Kind of like what I’ve heard described as “an act of God” but I don’t care for that phrase. Is there a word for this? Thanks!
A single word could be chance. Merriam-Webster has
1 a: something that happens unpredictably without discernible human intention or observable cause
1 b: the assumed impersonal purposeless determiner of unaccountable happenings
1 c: the fortuitous or incalculable element in existence
I was saved from drowning at sea by a chance encounter with a fishing boat.
Weather Vane has provided a solid suggestion.
Judging from the opening line of you query, though, it might be that you're looking for a word that connotes "the belief that some things just happen", i.e. the belief in chance.
If this is the case, I reckon accidentalism is a nice alternative:
In philosophy, accidentalism denies the causal closure of physical determinism and maintains that events can succeed one another haphazardly or by chance (not in the mathematical but in the popular sense).