You should know how to shoot one handed and make sure that you don't limp wrist etc. while you should know how to use your weak hand , I would not over think it and spend a long time practicing weak hand. I would much rather spend my time getting faster or shooting strong hand with a flash light in the weak hand.

9 mm is plenty adequate for stopping threats

At least for me the actions of "practicing shooting with the weaker hand" was just pretending to practice. Even taking a couple offhand courses was not the magic. Before each course I only shot the weaker hand (left hand in my case) for 4-6 weeks. This is with a mirror image left hand holster That would be 100 rounds per session and 2 sessions a week. It was only then that the instructor could identify my strengths and weaknesses and help me improve.

Here are a few of the big things I learned with the Glock 17/19. Being VERY right eye dominant I had to close the right eye when point shooting. I also shot sights better with only the left eye open ... and that took a while to get everything to adjust. Eye dominance is a big deal. It turns out that I reload the Glock's surer and faster left handed. Even shooting strong hand (right) I often reload left handed. There are lots of big and little differences here and I was only able to learn them by shooting in this full immersion technique followed by good instruction.

When I was a kid I broke my right arm. After 3 months in a cast I could do most things just as well left handed. Same thing.

'hit rate for the FBI agents was abysmal'
I was at old Remy range DFW yrs ago, Gov squad came in. Not very good shots! Aim, trigger pull and recoil is what needs practice, dry fire doesn't cut it. You probably need the second shot!

https://www.firearmsnews.com/editorial/fbi-miami-firefight-part1/486108

There was some cold hard lessons learned that day, having to shoot with your off hand being just one of them. That day was a major awakening for Law Enforcement and changed it for ever.

Getting off the X is critical. IMO, practicing your draw, with different types of clothing on is also way up there on the must practice list. When you are out and about you can practice finding places for cover or concealment, even if you are with family.. Practice getting the piece out while getting off of the X, even if it's only 5 or 10 feet helps too. JMO.

Yes, always run atleast a couple magazines 1 handed at the range. My non dominant had has a birth defect, I can’t reach the trigger with it, so hopefully I never lose function of my dominant hand.

I was taught to shoot handguns by an old top notch competition bullseye shooter. He would say, "If a handgun was meant to be shot with two hands it would have two handles on it",

+1

I shot maybe 5-10% one handed, be it dominant or non.Wish I did more! I’m currently sitting on the couch in a sling dry firing a 642 with my “good” non-dominant hand and 2 things I notice, 1. not as steady as my right hand and 2. My hand fatigues quicker.

When you actually lose access your dominant hand/arm, you realize how dependent you are to it. Definitely a wake up call for me to train ambidextrously on essential tasks, not just shooting.

Definitely good to train as much as your circumstance allows with your strong side (no support hand) and your 'weak' hand (unsupported).

I am fortunate to have my own private shooting range on my property, so I can run whatever 'drills' I feel like. But I routinely devote some practice time to 'weak hand' shooting and unsupported strong side shooting.

Most public shooting ranges don't allow for things like 'rapid fire', shooting on the move, from behind barricades/cover etc....

You can get some decent experience shooting IDPA (available to a lot of folks).....or take some dedicated self defense classes (not available everywhere).

On my own range....I can practice pistol defense on steel or cardboard targets, set them up however I like. Practice shooting on the move, advancing, retreating, from angles, from behind cover or concealment. From a vehicle, from disadvantaged positions.

Practice reloads and malfunction drills. Perform reloads from various positions and with simulated constraints. Add pressure by using time limits. Engage multiple targets, do transition drills etc...

My range is 100 yds. by 100 yds. (wide and long) and covered in gravel. So plenty of room to set up scenarios and take longer than normal shots.

Again, I am fortunate to be able to practice things that most folks are not. But that doesn't mean you can't train yourself at home (safely) to do things like draw and present your weapon with your weak hand (can your even reach it).

Perform a reload with only one hand (though reloads are seldom needed by non-LEO). Malfunction drills are IMPORTANT. I can't tell you the number of people 'novices' I've had on my range that when they experience a stoppage are just dead in the water (just stop and stare at the firearm). No clue how to clear it.

Lots of things can be practiced with an UNLOADED weapon (or using snap caps) in your own home. Enough to at least have you 'thinking' about what you might do in certain situations.