I use a g19 and I swapped the mag release and am forced to slingshot the slide till the new ambi gens come out.
Ar pattern rifles that’s tricky, you can get all the ambi controls for a right hand rifle.
Even left hand ar uppers come with right hand lowers but an ambi mag release, selector but oddly use a right hand charging latch.
Stag arms has lots of options to pick from, some makers like kac have ambi controls but iirc the bolt lock on one side is just a release.
Shotguns, a friend of mine he’s a lefty as well and out of the 5 shotguns he’s let me fondle I’ve had no problem operating them I’d go for the gun model that has ejection out the bottom.
I think it was a Browning bps, really nice but even with my long arms it’s a stretch for the pump.
He’s got a Mossberg that the pump is a bit longer on the backside so it’s not as bad a reach and the problem for me is I get shells in the arm and that sucks.
You can get left hand bolt guns or shoot like the guy from saving private ryan.
I’d always try to find a left hand option if you are a lefty, the left hand on right hand gun will slow you down during reloads.
You get much more gas in face with RH rifles in the LH, in the AR you can use the right hand to remove the mag with a hand and dump/put away. Reach for a reload then use your left hand to reach for the paddle and your back on target.
I hate this method, I prefer to reach for a new mag, grab the old and insert the new then back on target while the one hand puts the old mag away or dump it.
There are several videos on YouTube that help lefties find a method of use for rh rifles but I always go for the left hand option is available.