Finding voter fraud is like trying to teach chickens about pi. There aren't really any systems around to detect it, the system itself isn't designed to make it detectable. Fraud obviously by its nature tries to remain hidden and the people in charge of detecting it are academics who are almost universally on the side that wants to Republicans to lose so they're generally disinterested in digging. So all we really have to go on are anecdotes
I'm really not an expert on what is or isn't going on all I can say on my end is that in my experience there is nothing much that I can see in terms of safeguards. Precovid, in my state you could register with a guy right off the street with no documentation if I remember correctly, The main safeguard was a big folder with all the registered voters listed where you'd have to show your id and they'd cross it off and this was more than what I've heard is present in other areas where you don't need any id at all. Even preCOVID also have whats known as vote harvesting where third parties go around collecting ballots from people many of whom were also registered in the same fashion. You can see where things can go shady with this.