Do I stand any chance in a race? Unfortunately, I know I'll be at a disadvantage in racing because I haven't been able to find or create a team, as all of the other people I know who are into cycling are men. I weigh 146 lbs, and my bike weighs 19 lbs. I can sustain 18 mph on my solo rides, some stats on some recent notable efforts of mine:
on a -3.8 incline I averaged 36 mph for 0,4 miles, about 325 watts in-the saddle, and another sprint, at 0% incline, I averaged 480 watts in the saddle for 0,2 miles. How might I measure up in a cat 4 peloton, especially without the help of a team?
Answer:  reset your expectations and give it a go.
The first race I entered, my only goal was to finish.  Second time I did it, the goal was to pace better and finish with a better time than my first effort.
After that, personal improvement is really the goal, developing racecraft and strategy.
When riding in a group/bunch/peloton/paceline of cyclists, you won't believe the amount of boost received from the draught.  Simply watch and learn, parrot what others do, and listen to any advise offered.
It would be good if you could do some group riding before a proper race.  Look for a publicised group ride and try to join.  It can be hard to ride close enough behind someone to benefit from the aero gains, and it can be unnerving to be followed closely by someone.  Practice will help.
Even if you fall off the back of a group in short order, you'll experience what group riding is like.  It can be addictive!

If you possibly can, ride the race route beforehand.  Even some of it is better than going into it cold.  Use an app like Strava etc to log a time, and expect that a bunch ride will drop your time by about 20% assuming similar weather.
Gender is relatively irrelevant in a race - different categories are all run at the same time, perhaps with a few minutes gap between the start times.  IE the full length race might start at 0800 with the half-length version leaving at 0810.   So there's always some mixing between classifications whether they're age, distance, gender, or whatever the race organisers chose.
As a large middle age man, I'm able to descent faster than a lighter rider, but I have to work to maintain and carry that momentum up the next climb.   And then those lightweight little weeds pass me at triple my climbing speed.  Knowing what kind of road is coming up, whether its a long straight descent or a 20 minute climb helps you anticipate and pre-react.
Upshot  life's too short .  Get out and give it a go.  I've seen a guy in his 70's win his age group on a 1960s three-speed city bike.
You can't finish unless you start.