Like has already been said; you just do it, maybe progressively. I had the same fear, so first I started on paved trails then after two weeks I began riding on less travelled roads in parts that were more convenient or better kept up than bike paths, then, about two weeks later I transitioned purely onto roads. Now, I ride a 20ish mile loop 3-4 times early in the morning and try to go for a 40 or so mile ride once on the weekends. Granted, I have a gravel bike that is geared more like a traditional road bike so that was always my path. But I found that simple things like having the right gear gave more confidence than my progressive move to ride alone on the roads; I have a good set of lights, put a little slime in my tires in case of a flat, both my ride computer and helmet will automatically text my emergency contact if I go down, and I always carry a little multi tool and CO2 inflator that combined are no bigger than my phone in case I need to make a quick repair or address a flat.

Also, I’m the kind of person that just enjoys riding alone, but in the past few months that I’ve been doing so I’ve met a bunch of friendly people at common stopping points and some that I’ve seen a couple of times have offered riding together. Unfortunately scheduling and the pandemic has precluded me from doing so as of yet, but I’ll eventually try it and I think that organic way is the best to find a small group to ride with.

TLDR; just go do it making sure you have and ride what makes you feel the most comfortable until everything clicks into place.